High Dynamic Contrast Display System Having Multiple Segmented Backlight

ABSTRACT

In one embodiment, a display system includes a subpixelated display panel and a backlight array of individually controllable multi-color light emitters. When the display panel comprises a multi-primary subpixel arrangement having a white (clear) subpixel, the backlight control techniques allows the white subpixel to function as a saturated primary display color. In another embodiment, the display system may calculate a set of virtual primaries for a given image and process the image using a novel field sequential control employing the virtual primaries. In another embodiment, a display system comprises a segmented backlight comprising: a plurality of N+M light guides, said light guides forming a N×M intersections; a plurality of N+M individually addressable light emitter units, each of said N+M light emitter unit being associated with and optically connected to one of said N+M light guide respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application60/803,855 entitled COLOR IMAGING BACKLIGHT FOR COLOR DISPLAY SYSTEMSAND METHODS OF OPERATION, filed on Jun. 2, 2006, U.S. ProvisionalApplication 60/828,594 entitled DISPLAY SYSTEMS AND METHODS HAVINGDYNAMIC VIRTUAL PRIMARIES, filed on Oct. 6, 2006, and U.S. ProvisionalApplication 60/891,668 entitled HIGH DYNAMIC CONTRAST DISPLAY SYSTEMHAVING MULTIPLE SEGMENTED BACKLIGHT, filed on Feb. 26, 2007, which arehereby incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present application is related to display systems, and moreparticularly, to techniques for utilizing and controlling light from thebacklighting component in a display system.

BACKGROUND

Novel sub-pixel arrangements are disclosed for improving thecost/performance curves for image display devices in the followingcommonly owned United States patents and patent applications including:(1) U.S. Pat. No. 6,903,754 (“the '754 patent”) entitled “ARRANGEMENT OFCOLOR PIXELS FOR FULL COLOR IMAGING DEVICES WITH SIMPLIFIED ADDRESSING;”(2) United States Patent Publication No. 2003/0128225 (“the '225application”) having application Ser. No. 10/278,353 and entitled“IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS ANDLAYOUTS FOR SUB-PIXEL RENDERING WITH INCREASED MODULATION TRANSFERFUNCTION RESPONSE,” filed Oct. 22, 2002; (3) United States PatentPublication No. 2003/0128179 (“the '179 application”) having applicationSer. No. 10/278,352 and entitled “IMPROVEMENTS TO COLOR FLAT PANELDISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS FOR SUB-PIXEL RENDERING WITHSPLIT BLUE SUB-PIXELS,” filed Oct. 22, 2002; (4) United States PatentPublication No. 2004/0051724 (“the '724 application”) having applicationSer. No. 10/243,094 and entitled “IMPROVED FOUR COLOR ARRANGEMENTS ANDEMITTERS FOR SUB-PIXEL RENDERING,” filed Sep. 13, 2002; (5) UnitedStates Patent Publication No. 2003/0117423 (“the '423 application”)having application Ser. No. 10/278,328 and entitled “IMPROVEMENTS TOCOLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS WITH REDUCEDBLUE LUMINANCE WELL VISIBILITY,” filed Oct. 22, 2002; (6) United StatesPatent Publication No. 2003/0090581 (“the '581 application”) havingapplication Ser. No. 10/278,393 and entitled “COLOR DISPLAY HAVINGHORIZONTAL SUB-PIXEL ARRANGEMENTS AND LAYOUTS,” filed Oct. 22, 2002; and(7) United States Patent Publication No. 2004/0080479 (“the '479application”) having application Ser. No. 10/347,001 and entitled“IMPROVED SUB-PIXEL ARRANGEMENTS FOR STRIPED DISPLAYS AND METHODS ANDSYSTEMS FOR SUB-PIXEL RENDERING SAME,” filed Jan. 16, 2003. Each of theaforementioned '225, '179, '724, '423, '581, and '479 publishedapplications and U.S. Pat. No. 6,903,754 are hereby incorporated byreference herein in its entirety.

For certain subpixel repeating groups having an even number of subpixelsin a horizontal direction, systems and techniques to affectimprovements, e.g. polarity inversion schemes and other improvements,are disclosed in the following commonly owned United States patentdocuments: (1) United States Patent Publication No. 2004/0246280 (“the'280 application”) having application Ser. No. 10/456,839 and entitled“IMAGE DEGRADATION CORRECTION IN NOVEL LIQUID CRYSTAL DISPLAYS”; (2)United States Patent Publication No. 2004/0246213 (“the '213application”) (U.S. patent application Ser. No. 10/455,925) entitled“DISPLAY PANEL HAVING CROSSOVER CONNECTIONS EFFECTING DOT INVERSION”;(3) United States Patent Publication No. 2004/0246381 (“the '381application”) having application Ser. No. 10/455,931 and entitled“SYSTEM AND METHOD OF PERFORMING DOT INVERSION WITH STANDARD DRIVERS ANDBACKPLANE ON NOVEL DISPLAY PANEL LAYOUTS”; (4) United States PatentPublication No. 2004/0246278 (“the '278 application”) having applicationSer. No. 10/455,927 and entitled “SYSTEM AND METHOD FOR COMPENSATING FORVISUAL EFFECTS UPON PANELS HAVING FIXED PATTERN NOISE WITH REDUCEDQUANTIZATION ERROR”; (5) United States Patent Publication No.2004/0246279 (“the '279 application”) having application Ser. No.10/456,806 entitled “DOT INVERSION ON NOVEL DISPLAY PANEL LAYOUTS WITHEXTRA DRIVERS”; (6) United States Patent Publication No. 2004/0246404(“the '404 application”) having application Ser. No. 10/456,838 andentitled “LIQUID CRYSTAL DISPLAY BACKPLANE LAYOUTS AND ADDRESSING FORNON-STANDARD SUBPIXEL ARRANGEMENTS”; (7) United States PatentPublication No. 2005/0083277 (“the '277 application”) having applicationSer. No. 10/696,236 entitled “IMAGE DEGRADATION CORRECTION IN NOVELLIQUID CRYSTAL DISPLAYS WITH SPLIT BLUE SUBPIXELS”, filed Oct. 28, 2003;and (8) United States Patent Publication No. 2005/0212741 (“the '741application”) having application Ser. No. 10/807,604 and entitled“IMPROVED TRANSISTOR BACKPLANES FOR LIQUID CRYSTAL DISPLAYS COMPRISINGDIFFERENT SIZED SUBPIXELS”, filed Mar. 23, 2004. Each of theaforementioned '280, '213, '381, '278, '404, '277 and '741 publishedapplications are hereby incorporated by reference herein in itsentirety.

These improvements are particularly pronounced when coupled withsub-pixel rendering (SPR) systems and methods further disclosed in theabove-referenced U.S. patent documents and in commonly owned UnitedStates patents and patent applications: (1) United States PatentPublication No. 2003/0034992 (“the '992 application”) having applicationSer. No. 10/051,612 and entitled “CONVERSION OF A SUB-PIXEL FORMAT DATATO ANOTHER SUB-PIXEL DATA FORMAT,” filed Jan. 16, 2002; (2) UnitedStates Patent Publication No. 2003/0103058 (“the '058 application”)having application Ser. No. 10/150,355 entitled “METHODS AND SYSTEMS FORSUB-PIXEL RENDERING WITH GAMMA ADJUSTMENT,” filed May 17, 2002; (3)United States Patent Publication No. 2003/0085906 (“the '906application”) having application Ser. No. 10/215,843 and entitled“METHODS AND SYSTEMS FOR SUB-PIXEL RENDERING WITH ADAPTIVE FILTERING,”filed Aug. 8, 2002; (4) United States Publication No. 2004/0196302 (“the'302 application”) having application Ser. No. 10/379,767 and entitled“SYSTEMS AND METHODS FOR TEMPORAL SUB-PIXEL RENDERING OF IMAGE DATA”filed Mar. 4, 2003; (5) United States Patent Publication No.2004/0174380 (“the '380 application”) having application Ser. No.10/379,765 and entitled “SYSTEMS AND METHODS FOR MOTION ADAPTIVEFILTERING,” filed Mar. 4, 2003; (6) U.S. Pat. No. 6,917,368 (“the '368patent”) entitled “SUB-PIXEL RENDERING SYSTEM AND METHOD FOR IMPROVEDDISPLAY VIEWING ANGLES”; and (7) United States Patent Publication No.2004/0196297 (“the '297 application”) having application Ser. No.10/409,413 and entitled “IMAGE DATA SET WITH EMBEDDED PRE-SUBPIXELRENDERED IMAGE” filed Apr. 7, 2003. Each of the aforementioned '992,'058, '906, '302, 380 and '297 applications and the '368 patent arehereby incorporated by reference herein in its entirety.

Improvements in gamut conversion and mapping are disclosed in commonlyowned United States patents and co-pending United States patentapplications: (1) U.S. Pat. No. 6,980,219 (“the '219 patent”) entitled“HUE ANGLE CALCULATION SYSTEM AND METHODS”; (2) United States PatentPublication No 2005/0083341 (“the '341 application”) having applicationSer. No. 10/691,377 and entitled “METHOD AND APPARATUS FOR CONVERTINGFROM SOURCE COLOR SPACE TO TARGET COLOR SPACE”, filed Oct. 21, 2003; (3)United States Patent Publication No. 2005/0083352 (“the '352application”) having application Ser. No. 10/691,396 and entitled“METHOD AND APPARATUS FOR CONVERTING FROM A SOURCE COLOR SPACE TO ATARGET COLOR SPACE”, filed Oct. 21, 2003; and (4) United States PatentPublication No. 2005/0083344 (“the '344 application”) having applicationSer. No. 10/690,716 and entitled “GAMUT CONVERSION SYSTEM AND METHODS”filed Oct. 21, 2003. Each of the aforementioned '341, '352 and '344applications and the '219 patent is hereby incorporated by referenceherein in its entirety.

Additional advantages have been described in (1) United States PatentPublication No. 2005/0099540 (“the '540 application”) having applicationSer. No. 10/696,235 and entitled “DISPLAY SYSTEM HAVING IMPROVEDMULTIPLE MODES FOR DISPLAYING IMAGE DATA FROM MULTIPLE INPUT SOURCEFORMATS”, filed Oct. 28, 2003; and in (2) United States PatentPublication No. 2005/0088385 (“the '385 application”) having applicationSer. No. 10/696,026 and entitled “SYSTEM AND METHOD FOR PERFORMING IMAGERECONSTRUCTION AND SUBPIXEL RENDERING TO EFFECT SCALING FOR MULTI-MODEDISPLAY” filed Oct. 28, 2003, each of which is hereby incorporatedherein by reference in its entirety.

Additionally, each of these co-owned and co-pending applications isherein incorporated by reference in its entirety: (1) United StatesPatent Publication No. 2005/0225548 (“the '548 application”) havingapplication Ser. No. 10/821,387 and entitled “SYSTEM AND METHOD FORIMPROVING SUB-PIXEL RENDERING OF IMAGE DATA IN NON-STRIPED DISPLAYSYSTEMS”; (2) United States Patent Publication No. 2005/0225561 (“the'561 application”) having application Ser. No. 10/821,386 and entitled“SYSTEMS AND METHODS FOR SELECTING A WHITE POINT FOR IMAGE DISPLAYS”;(3) United States Patent Publication No. 2005/0225574 (“the '574application”) and United States Patent Publication No 2005/0225575 (“the'575 application”) having application Ser. Nos. 10/821,353 and10/961,506 respectively, and both entitled “NOVEL SUBPIXEL LAYOUTS ANDARRANGEMENTS FOR HIGH BRIGHTNESS DISPLAYS”; (4) United States PatentPublication No. 2005/0225562 (“the '562 application”) having applicationSer. No. 10/821,306 and entitled “SYSTEMS AND METHODS FOR IMPROVED GAMUTMAPPING FROM ONE IMAGE DATA SET TO ANOTHER”; (5) United States PatentPublication No. 2005/0225563 (“the '563 application”) having applicationSer. No. 10/821,388 and entitled “IMPROVED SUBPIXEL RENDERING FILTERSFOR HIGH BRIGHTNESS SUBPIXEL LAYOUTS”; and (6) United States PatentPublication No. 2005/0276502 (“the '502 application”) having applicationSer. No. 10/866,447 and entitled “INCREASING GAMMA ACCURACY IN QUANTIZEDDISPLAY SYSTEMS.”

Additional improvements to, and embodiments of, display systems andmethods of operation thereof are described in: (1) Patent CooperationTreaty (PCT) Application No. PCT/US 06/12768, entitled “EFFICIENT MEMORYSTRUCTURE FOR DISPLAY SYSTEM WITH NOVEL SUBPIXEL STRUCTURES” filed Apr.4, 2006, and published in the United States as United States PatentApplication Publication 200Y/AAAAAAA; (2) Patent Cooperation Treaty(PCT) Application No. PCT/US 06/12766, entitled “SYSTEMS AND METHODS FORIMPLEMENTING LOW-COST GAMUT MAPPING ALGORITHMS” filed Apr. 4, 2006, andpublished in the United States as United States Patent ApplicationPublication 200Y/BBBBBBB; (3) U.S. patent application Ser. No.11/278,675, entitled “SYSTEMS AND METHODS FOR IMPLEMENTING IMPROVEDGAMUT MAPPING ALGORITHMS” filed Apr. 4, 2006, and published as UnitedStates Patent Application Publication 2006/0244686; (4) PatentCooperation Treaty (PCT) Application No. PCT/US 06/12521, entitled“PRE-SUBPIXEL RENDERED IMAGE PROCESSING IN DISPLAY SYSTEMS” filed Apr.4, 2006, and published in the United States as United States PatentApplication Publication 200Y/DDDDDDD; and (5) Patent Cooperation Treaty(PCT) Application No. PCT/US 06/19657, entitled “MULTIPRIMARY COLORSUBPIXEL RENDERING WITH METAMERIC FILTERING” filed on May 19, 2006 andpublished in the United States as United States Patent ApplicationPublication 200Y/EEEEEEE (referred to below as the “Metamer Filteringapplication”.) Each of these co-owned applications is also hereinincorporated by reference in their entirety.

A display system with a light emitting component or source, referred toas a backlight, functions as a dynamic light modulation device thatabsorbs or transmits optical energy from the light emitting source inorder to provide images for viewing by a user. A backlit liquid crystaldisplay (LCD) device is an example of such a display system. The opticalenergy emitted by the light emitting source is the active source oflight that creates the displayed image seen by a user viewing an imageon the display panel of an LCD. In display systems that utilize colorfilters to produce the colors in an image, the typically relativelynarrow band color filters subtract optical energy from the light emittedby the display system's light emitting source to create the appearanceof colors. The color filters are disposed on the display panel tocorrespond to various sub-pixel layouts such as those described in theapplications referenced above, including those illustrated in FIGS. 3and 6-9 herein. It has been estimated that as little as four to tenpercent (4-10%) of the illumination from a backlight source is actuallyemitted from the display as light viewed by the viewer of the image. Inan LCD display, the TFT array and color filter substrate are typicallythe largest illumination barriers.

Arrays of light emitting diodes (LEDs) are used as light emittingsources in backlit display systems. U.S. Pat. No. 6,923,548 B2 disclosesa backlight unit in a liquid crystal display that includes a pluralityof lamps or chips arranged such that LED chips realizing R, G, and Bcolors are built in the respective lamps or chips. U.S. Pat. No.6,923,548 B2 describes the backlight unit as realizing high brightnessand providing a thin backlight unit. U.S. Pat. No. 7,002,547, which ishereby incorporated by reference herein, discloses a backlight controldevice for a transmissive type or for a transreflective type liquidcrystal display equipped with LEDs as a backlight. The backlight controldevice includes an LED driving circuit connected to a power supplycircuit for driving the LED, and a current control device that detectsbrightness around the liquid crystal display for controlling the drivingcurrent for the LED according to the detected brightness. Hideyo Ohtsukiet al., in a paper entitled “18.1-inch XGA TFT-LCD with wide colorreproduction using high power led-backlighting,” published in the Proc.of the Society for Information Display International Symposium, in 2002,disclose an 18.1 inch XGA TFT-LCD module using an LED-backlighting unitOhtsuki et al disclose that a side-edge type backlight is applied andtwo LED strips are located on the top and bottom edges of a light-pipe.Each LED strip arranges multiple red, green and blue LEDs. The lightsfrom the red, green and blue LEDs are mixed and injected into thelight-pipe. The brightness of the red, green and blue LEDs can be dimmedindependently by a control circuit. Ohtsuki et al. disclose that thecolor-filter of this LCD panel is well-tuned to get higher colorsaturation.

U.S. Pat. No. 6,608,614 B1 entitled “Led-based LCD backlight withextended color space” discloses a backlight for a liquid-crystal displaythat includes a first LED array that provides light with a firstchromaticity and a second LED array that provides light with a secondchromaticity. A combining element combines the light from the first LEDarray and the second LED array and directs the combined light toward theliquid crystal display. A control system is operationally connected tothe second LED array. The controller adjusts the brightness of at leastone LED in the second LED array to thereby adjust the chromaticity ofthe combined light.

US 2005/0162737 A1 (hereafter, “the '737 publication)”, entitled “HighDynamic Range Display Devices,” discloses a display having a screenwhich incorporates a light modulator and which is illuminated with lightfrom a light source comprising an array of controllable light-emitters.The controllable-emitters and elements of the light modulator may becontrolled to adjust the intensity of light emanating from correspondingareas on the screen. FIG. 15 shows a section through a display 60 inwhich a rear-projection screen 53 comprising a diffusing layer 22 isilluminated by an array 50 of LEDs 52. The brightness of each LED 52 iscontrolled by a controller 39. Screen 53 includes a light modulator 20.The rear face of light modulator 20 is illuminated by LED array 50. FIG.14 is a schematic front view of a portion of display 60 for a case wherecontrollable elements (pixels) 42 of light modulator 20 correspond toeach LED 52. Each of the controllable elements 42 may comprise aplurality of colored sub-pixels. The '737 publication discloses thatLEDs 52 may be arranged in any suitable manner, and shows two likelyarrangements of LEDs 52 as being rectangular and hexagonal arrays. Adiffuser 22A in conjunction with the light-emitting characteristics ofLEDs 52 causes the variation in intensity of light from LEDs 52 over therear face of light modulator 20 to be smooth. The '737 publicationfurther discloses that light modulator 20 may be a monochrome lightmodulator, or a high resolution color light modulator. Light modulator20 may comprise, for example, a LCD array. The '737 publicationdiscloses that display 60 can be quite thin. For example, display 60 maybe 10 centimeters or less in thickness. US 2005/0162737 A1 is herebyincorporated by reference herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The organization and methods of operation of the display systems andtechniques disclosed herein are best understood from the followingdescription of several illustrated embodiments when read in connectionwith the following drawings in which the same reference numbers are usedthroughout the drawings to refer to the same or like parts:

FIG. 1A is a block diagram of selected components of a first embodimentof a multi-primary display system with a first backlight array ofmulti-color light emitters;

FIG. 1B is a block diagram of an example of a peak down samplingfunction block that may be used in the embodiment illustrated in FIG.1A;

FIG. 2A is a block diagram of a selected components of a secondmulti-primary display system with a second backlight array ofmulti-color light emitters;

FIG. 2B is a block diagram of an example of a peak down samplingfunction block that may be used in the embodiment illustrated in FIG.2A;

FIG. 3 shows an eight subpixel repeating group for a four color displaypanel;

FIG. 4 shows a portion of a backlight array having light emitters inthree colors;

FIG. 5 shows a portion of a backlight array having light emitters infour colors;

FIG. 6 shows a portion of a four color display panel that includes a sixsubpixel repeating group;

FIG. 7 shows a portion of a six color display panel that includes a sixsubpixel repeating group;

FIG. 8 shows a portion of a display panel that includes a two subpixelrepeating group using square subpixels in two colors;

FIG. 9 shows a portion of a display panel that includes a sixteensubpixel repeating group using rectangular subpixels in five colors;

FIG. 10 is a block diagram of a liquid crystal display system in whichthe backlight control techniques and methods disclosed herein may beimplemented;

FIG. 11 is a diagrammatic representation illustrating the use of theinput image data to determine the value of a light emitter in thebacklight array;

FIG. 12 is a diagrammatic representation illustrating the operation ofthe backlight interpolation function to produce a low resolution imagefrom the light from the light emitters in the backlight array;

FIG. 13 shows an exemplary display panel having a multi-primary subpixelrepeating group with a white (clear) subpixel and illustrating how thewhite subpixel is used as a primary color that is determined by thebacklight control techniques illustrated and described herein;

FIG. 14 is a portion of a prior art display in which a rear-projectionscreen comprising a diffusing layer is illuminated by an array of lightemitting diodes (LEDs).

FIG. 15 is a schematic front view of a portion of the prior art displayof FIG. 14 for a case where controllable elements (pixels) of the lightmodulator correspond to each LED.

FIG. 16 is a CIE 1931 color chart showing a backlight LED gamut and anindividual image gamut map smaller than the backlight LED gamut.

FIG. 17 shows the backlight LED gamut of FIG. 16 with three virtualprimaries and a given color within the virtual primary gamut.

FIG. 18 is a block diagram of a hybrid system with both spatial andvirtual primary means of adjusting the LED backlight and LCD values.

FIGS. 19A and 19B are diagrammatical representations of the two methodsof reconstructing a given color by the system shown in FIG. 18

FIGS. 20A, 20B, and 20C are diagrammatical representations of methods ofusing virtual primaries.

FIG. 21A is a block diagram of a virtual primary field sequential colorsystem.

FIG. 21B is an alternative embodiment of the Calc Virtual Primariesmodule of FIG. 21A

FIG. 22 is a diagram showing two embodiments of the bounding box moduleof FIG. 21A

FIG. 23 is a CIE 1931 color chart with superimposed XYZ primariesshowing a multiprimary backlight LED gamut and an individual image gamutmap smaller than the multiprimary backlight LED gamut.

FIG. 24 shows a portion of a display panel that includes a twelvesubpixel repeating group using rectangular subpixels in five colors.

FIG. 25 depicts one embodiment of a novel segmented backlight for use ina display.

FIG. 26 depicts a conventional backlight comprising a light guide andtwo emitters.

FIG. 27 depicts one embodiment of an improved backlight over theconvention backlight of FIG. 26.

FIG. 28 depicts a conventional backlight comprising a light guide andfour emitters.

FIG. 29 depicts one embodiment of an improved backlight over theconvention backlight of FIG. 28.

FIG. 30 depicts another embodiment of a novel segmented backlight foruse in a display.

FIG. 31 shows a cross sectional view of across one light guide in oneembodiment of a novel segmented backlight.

FIGS. 32A and 32B depict two display systems comprising novel segmentedbacklights in connection with a monochrome and a multiprimary coloredfront panel respectively.

FIG. 33 depicts a display system comprising a novel segmented backlightin connection with a hybrid virtual primary-field sequential controlsystem and methodology.

DETAILED DESCRIPTION

The use of an array of light emitters, such as light emitting diodes(LED), as a backlight in a subpixelated display system generallyprovides higher purity color points that can be filtered for reasonablyhigh color purity on the display when compared to other backlighttechnologies. However, since contrast is not infinite (i.e., the blacklevel is not perfectly black) in some types of display panels (e.g.,LCDs), there is typically some bleed of color from the off-statesubpixels that will limit the saturation of the color. In addition, thecolor filters themselves may not have good color purity, and may allowsome unwanted light to pass through from other colored light emitters.In a display system in which the individual light emitters disposed in abacklight array can be independently addressed, adjustment of the colorof the backlight is possible. This ability to adjust the color of thebacklight provides an additional degree of freedom that may be used toincrease the dynamic range and color purity of the display. It may alsoincrease the effectiveness of the subpixel rendering algorithms byoptimizing the spread of luminance information on the display panelsubpixels with the color temperature, either globally or locally, of thelight emitted from the backlight array.

The discussion proceeds now to an overview of the components of thedisplay system, followed by a description of techniques for controllingthe backlight array, and concluding with a discussion of techniques forimplementing backlight control that show the interaction among aspectsof the human vision system, the colors in the particular image beingdisplayed and the particular subpixel layout of the display panel.

In the discussion that follows, a display system includes a displaypanel on which color images are formed by combining the individualcolors disposed on a color filter substrate in an arrangement, orlayout, referred to as a subpixel repeating group. The term “primarycolor” refers to each of the colors that occur in the subpixel repeatinggroup. When a subpixel repeating group is repeated across a displaypanel to form a device with the desired matrix resolution, the displaypanel is said to be substantially comprised of the subpixel repeatinggroup. In this discussion, a display panel is described as“substantially” comprising a subpixel repeating group because it isunderstood that size and/or manufacturing factors or constraints of thedisplay panel may result in panels in which the subpixel repeating groupis incomplete at one or more of the panel edges. By way of example, adisplay panel substantially comprised of a subpixel repeating group ofred, green and blue (RGB) colors disposed on the color filter substratein vertical columns (i.e., the conventional RGB stripe configuration)has three primary colors of red, green and blue, while a display panelsubstantially comprising subpixel repeating group 801 of FIG. 8including magenta subpixels 809, and green subpixels 808 has two primarycolors of magenta and green. Reference to display systems using morethan three primary subpixel colors to form color images are referred toas “multi-primary” display systems. In a display panel having a subpixelrepeating group that includes a white (clear) subpixel, the whitesubpixel represents a primary color referred to as white (W) or “clear”,and so a display system with a display panel having a subpixel repeatinggroup including RGBW subpixels is a multi-primary display system.

The term “emitter” is sometimes used in earlier ones of theabove-referenced patent applications to refer to an individual subpixelof a particular color. In the discussion herein, “light emitter” refersto a light source disposed in the backlight array of the display system.The term “backlight-controlled (BC) primary color” refers to the colorof the light that passes through a white (W) subpixel that is producedby one or more light emitters in an array of light emitters functioningas a backlight in the display system.

First Embodiment of a Display System

FIG. 1A is a block diagram of an exemplary display system 100 having aspatial light modulator panel 160 for producing images Panel 160 is asubpixelated display panel substantially comprising a subpixel repeatinggroup 162 as shown, for example in any one of FIGS. 3, 6, 7, 8 and 9.FIG. 3 illustrates a subpixel repeating group 320 suitable for use onpanel 160. Subpixel repeating group 320 includes red subpixels 306,green subpixels 308, blue subpixels 310, and white (i.e., clear, with nocolor filter) subpixels 304. Many other variations of RGBW subpixelrepeating group 320 are possible, as described in US Patent ApplicationPublication 2005/0225574 referenced above. For example, subpixelrepeating group 620 of FIG. 6 comprises two red subpixels 606 and twogreen subpixels 608 on a checkerboard with white subpixel 604 and bluesubpixel 610 between them. Note that in the figures showing subpixelrepeating groups or portions of display panels showing subpixel layouts,the hatching lines used to represent the subpixel colors are usedconsistently across all figures.

It is understood that the techniques disclosed for controlling thebacklight of the display system as described below apply equally todisplay systems having different, fewer, or more colors than the RGBWsubpixel repeating group of FIG. 3. For example, FIG. 7 illustratesportion 700 of a six-color display panel having subpixel repeating group701 comprising red subpixels 706, green subpixels 708, large bluesubpixels 710, cyan subpixels 707 (shown in finer horizontal hatchinglines than the blue subpixels in these figures), magenta subpixels 709,and yellow subpixels 711 FIG. 9 illustrates a portion of a five-colorsubpixelated display panel substantially comprising subpixel repeatinggroup 902 having sixteen (16) subpixels of red subpixels 906, greensubpixels 908, blue subpixels 910, and cyan subpixels 912 with whitesubpixels interspersed.

It is also to be understood that the techniques disclosed for utilizingthe backlight of the display system as described below apply equally todisplay systems having as few as two primary colors. For example, FIG. 8illustrates portion 800 of a two-color display panel having subpixelrepeating group 801 comprising magenta subpixels 809, and greensubpixels 808. Display panel 160 of FIG. 1A may substantially comprisesubpixel repeating group 801.

With reference again to FIG. 1A, exemplary display system 100 furtherincludes an array 120 of light emitting sources 122 used as a backlightfor panel 160. Array 120 may be comprised of light emitters 122 indifferent colors, each of the emitters being independently addressableunder electronic control such that the control of each individual colormay be completely separated from control of each of the other colors inarray 120. The array 120 of light emitting sources may comprise lightemitting diodes (LEDs) or other types of light emitters that are capableof being independently addressable and controlled. For example, a colorflat panel display of any type may be used, such as a second LCD, anOrganic Light Emitting Display (OLED), Plasma Display Panel (PDP), aRear Projection Television (RPTV and the like), or even a Cathode RayTube (CRT).

FIGS. 4 and 5 illustrate portions of two layouts for array 120 of lightemitters that may be useful as backlights. FIG. 5 shows a portion of anoffset, or hexagonal, array 500 of red 506, green 508, and blue 510(RGB) light emitters. Light emitter array 500 is suitable for use as abacklight for an RGB display panel, and is also suitable for use as abacklight for an RGBW panel having a subpixel arrangement of the typeillustrated in FIG. 3 or 6, or according to any one of the various RGBWlayouts illustrated and described in US Patent Application Publication2005/0225574 referenced above.

FIG. 4 shows a portion of a rectangular array 400 of red 406, green 408,blue 410, and cyan 412 light emitters, referenced hereafter as RGBClight emitters. Cyan may also be referred to as the color emerald. Lightemitter array 400 is suitable for use as a backlight for a display panelsubstantially comprised of an RGBC subpixel repeating group, or for adisplay panel substantially comprised of an RGBCW subpixel repeatinggroup such as, for example, subpixel repeating group 902 of FIG. 9.Light emitter array 400 with four different colors of light emitters isalso suitable for use as a backlight for a display panel substantiallycomprised of an RGBW subpixel repeating group; when so used, lightemitter array 400 allows the substantially green subpixel to shift tobeing substantially cyan (or emerald) if the pass band of the greensubpixel includes both the green and cyan emitter emission wavelengths.

While the portions of light emitter arrays 400 and 500 illustrated inFIGS. 4 and 5 by way of example have rectangular and hexagonalarrangements of light emitters, respectively, it is understood thatother arrangements are possible and suitable for implementing thebacklight control techniques described in more detail below. All suchpossible and suitable layouts are contemplated as being included in theimplementation of the backlight control techniques discussed herein.Additional discussion follows below about the interactions among thelight emitters, the colors in the image being displayed and theparticular subpixel layout of the display panel. Information about theresolution of array 120 of light emitting sources (FIG. 1) is deferredto that discussion.

With reference again to FIG. 1A, display system 100 illustrates two datapaths for input RGB image data 102. The first RGB image data pathincludes input gamma (linearization) module 105, gamut mapping (GMA)function 140, subpixel rendering (SPR) module 150, and output inversegamma module 115, producing output image data for display on panel 160.In display systems described in various ones of the co-ownedapplications noted and incorporated by reference above, the GMA functiontransforms input color data specified in RGB primaries to amulti-primary target color space, such as, for example, RGBW. The outputof the GMA function is a set of input image color values in RGBW colorspace, with a luminance, L, component identified. For information aboutthe operation of gamut mapping functions in general, see, for example,US Published Patent Applications 2005/0083352, 2005/0083341,2005/0083344 and 2005/0225562.

In display system 100, GMA function 140 generates a requantized imagefor display on panel 160 using the output of the function designated“X/X_(L)” in box 136, which in turn receives the input RGB image valuesfrom input gamma operation 105 as well as input values labeledR_(L)G_(L)B_(L) produced by Backlight Interpolation function 130. TheBacklight Interpolation function 130 and X/X_(L) function 136 aredescribed in further detail below GMA function 140 may utilize any ofthe gamut mapping algorithms disclosed in the above references orotherwise known in the art or yet to be discovered. In the case of adisplay system producing images on a display panel having an RGBWsubpixel repeating group, GMA function 140 utilizes an RGB to RGBWalgorithm.

With continued reference to the first data path in FIG. 1A, the set ofgamut-mapped input image color values (e.g., RGBWL) produced by GMAfunction 140 is then input to subpixel rendering function 150. Forinformation about the operation of SPR function 150, see, for example,US Published Patent Applications 2003/0034992, 2003/0103058,2003/0085906, 2005/0225548 and 2005/0225563. Note that the downwardarrow in box 150 of FIG. 1A signifies that the SPR function here isperforming a down sampling function, there being fewer color subpixelsin the display than the number of color samples from the GMA function.The output values (e.g., RGBW) of SPR function 150 are then input tooutput gamma function 115 which produces output image data values fordisplay on panel 160.

Backlight Control Functions

With continued reference to FIG. 1A, RGB input data 102 in displaysystem 100 also proceeds along a second data path that integrates theoperation of backlight array 120 of light emitters into the ultimatedisplay of the output image. The second data path includes Peak Functionblock 110, which computes values for individual light emitters in array120. Backlight Interpolation Function 130 uses the values of the lightemitters to compute the distribution of light of each color at eachpixel overlying light emitter array 120. The output of BacklightInterpolation Function 130, designated as R_(L)G_(L)B_(L) in FIG. 1A,is, in effect, a filtered version of the RGB input image data thatapproximates the distribution of light from light emitter array 120.Each of these functions 110 and 130 will now be described in moredetail.

Peak Function block 110 determines the values for light emitters inarray 120 using RGB input image data 102. An example of a simpleimplementation of Peak Function 110 may be Max(V_(PSF)). This sets thevalue, V, of the light emitter of a given color to be equal to themaximum (peak) value of that color channel in the original input image(after any gamma pre-conditioning performed in input gamma module 105)in the local area of the light emitter's Point Spread Function (PSF)support. The algorithm used in Peak Function block 110 may be a form ofdown sampling (indicated by the downward arrow in block 110 in FIG. 1A)whose output values for a given light emitter are the peak values of theinput image data in an area bounded by the neighboring light emitters ofthe same color.

FIG. 11 is a simplified diagram illustrating the interaction of thelight emitters and the input image data in display system 100 FIG. 11shows a portion of array 120 of light emitters, including light emitters124 and 126. A diagrammatic representation 103 of RGB input image data102 of FIG. 1A (after being processed by input gamma function 105) showsthe input image data arranged in an array of input color valuesoverlying array 120 of light emitters. The point spread function oflight emitter 124 indicates a coverage area 130 of the light from lightemitter 124, shown in dashed lines and bounded by line 131, whichcorresponds to an image portion 104 of the input image color data asrepresented in diagrammatic representation 103. Light from light emitter124 has to have an illumination level sufficient to provide light forthe brightest input color data value in image portion 104. The pointspread function of light emitter 124 overlaps with the point spreadfunction of light emitter 126, as shown by the dashed lines of the twoareas 130 and 132, and thus some of the input image color values used todetermine the value of light emitter 124 are also used to determine thevalue of light emitter 126.

Table 1 provides an example of a Peak Function, called “dopeak,” inpseudo code that uses the maximum value of the input image region todetermine the value for one light emitter. For simplicity ofillustration, this peak function makes the assumptions that the outputdisplay panel has a resolution of 8 times that of the backlight array,that the backlight array includes red, green and blue light emittersdisposed in a rectangular (or square) array, and that the red, green andblue light emitters are coincident.

TABLE 1 Pseudo-Code for Peak Function, “dopeak” function dopeak (x,y)build backlight image local r,g,b local Rp,Gp, Bp = 0,0,0 local i,j fori=0, 15 do find the peak value for j=0,15 do r,g,b =spr.fetch(“ingam”,x*8+1−4,y*8+j−4) Rp = math.max(Rp,r) Gp =math.max(Gp,g) Bp = math.max(Bp,b) end end spr.store(“led”,x,y,Rp,Gp,Bp)endThose skilled in the art will appreciate that other, more sophisticateddown sampling algorithms may also be employed, such as those based on async or windowed sync function, or other functions known in the art oryet to be discovered. All such possible down sampling functions arecontemplated as being suitable for the backlight control techniquesdisclosed herein.

In Table 1, the spr.fetch function represents the fetching or arrival ofdata from the previous step, for example from input gamma module 105 ofFIG. 1A. The spr.store function represents storing or passing data on tothe next step, such as backlight array values 112 being stored in LEDarray 122. Note that the pseudo code in table 1 may fetch the inputvalues in “random access” mode which may ultimately result in fetchingeach value several times while storing each output value in order. Thismay be an appropriate technique for implementations in software. Inhardware, it may use fewer gates to process the inputs in order as theyarrive, holding them in input line buffers until enough are available tocalculate output values. Alternately, it may use fewer gates to processthe inputs in the order they arrive while storing intermediate outputresults in output line buffers until they are complete.

The output of Peak Function 110 is a value for each light emitter inarray 120 indicating the illumination level of the light emitter. Theselight emitter values are input to a backlight array controller (notshown) for subsequent illumination of backlight array 120 when theoutput image is displayed on panel 160.

FIG. 12 is a simplified diagrammatic representation illustrating theinteraction of the light emitters and the output image data in displaysystem 100. Backlight Interpolation Function 130 uses the value of eachlight emitter 124 in backlight array 120, as established in PeakFunction block 110, to calculate the distribution of light of each colorat each output pixel 164 in display panel 160 overlying light emitter124. This distribution is interpolated from the values of the lightemitters established in Peak Function block 110, taking into account thepoint spread function (PSF) of each light emitter 124 in array 120 andthe presence of diffusers 136 and other optical components. Thisoperation is an “up sampling” function, as indicated by the up arrow,and many possible “up sampling” functions may be suitable. One suchfunction is a summation of the point sample contribution of the PSFs ofthe local light emitters times their values computed by the downsampling Peak function 110.

Table 2 provides pseudo-code for a backlight interpolation functioncalled “dointerp” This function fetches from a memory area called“ledbuf” (LED buffer) and writes to memory area for storing output colorvalues called “fuzbuf.” The function “dointerp” is called once for eachinput pixel and calculates the effect of all the surrounding backlightpoint spread functions to produce the color value that would be seenunder the input (logical) pixel. The “dointerp” function uses a pointspread function for each light emitter that assumes that each pixel canonly be affected by the surrounding four light emitters.

TABLE 2 Pseudo-Code for Backlight Interpolation Function, “dointerp”function dointerp(x,y) build the effective backlight image local xb,yb =math.floor(x/8),math.floor(y/8) position of a nearby backlight localxd,yd = spr.band(x,7),spr.band(y,7) distance to a nearby LED centerlocal r,g,b color of the backlight centers local rs,gs,bs=0,0,0 sum ofthe overlapping backlight point spread functions local psf point spreadfunction for current pixel and LED r,g,b = spr.fetch(ledbuf,xb−1,yb−1)get LED center color psf = math.floor(spread[xd]*spread[yd]/4096)calculate point spread function here rs = rs + r*psf sum upper left LEDgs = gs + g*psf bs = bs + b*psf r,g,b = spr.fetch(ledbuf,xb,yb−1) colorof upper right LED psf = math.floor(spread[7−xd]*spread[yd]/4096) PSFfor this led and pixel rs = rs + r*psf sum upper left LED gs = gs +g*psf bs = bs + b*psf r,g,b = spr.fetch(ledbuf,xb−1,yb) color of lowerleft LED psf = math.floor(spread[xd]*spread[7−yd]/4096) PSF for this ledand pixel rs = rs + r*psf sum upper left LED gs = gs + g*psf bs = bs +b*psf r,g,b = spr.fetch(ledbuf,xb,yb) color of lower right LED psf =math.floor(spread[7−xd]*spread[7−yd]/4096) PSF for this led and pixel rs= rs + r*psf sum upper left LED gs = gs + g*psf bs = bs + b*psf rs =math.floor(rs/4096) sum was 12bit precision (+2 for 4 LEDs) gs =math.floor(gs/4096) colapse them back to 8bits bs = math.floor(bs/4096)spr.store(fuzbuf,x,y,rs,gs,bs); and save in output buffer end

The combination of the two functions, the “down sampling” of the PeakFunction 110 followed by the “up sampling” of the BacklightInterpolation Function 130 may retain the original resolution of theinput image in terms of sample count (image size), but produce a set ofoutput image values, designated as R_(L)G_(L)B_(L) in FIG. 1A, withlower spatial frequencies, i.e., a filtered version of the RGB inputimage data that approximates the distribution of light from lightemitter array 120. This data is then input to X/X_(L) function 136described below. Note that some images may have regions of uniform(i.e., the same) color values. Knowledge of the location of uniformcolor regions in the image may be used to reduce computational load inGMA function 140 by retaining/reusing values common to the region.

Prior to being input into GMA function 140, input image RGB data isfirst modified by the relationship between the brightness of eachincoming RGB value after input gamma function 105 and the actual amountof RGB light available at that given pixel from backlight array 120, asprovided by Backlight Interpolation function 130 (i.e., theR_(L)G_(L)B_(L) data values.) This modification is accomplished inX/X_(L) function 136 by the ratio, X/X_(L), where X is the incomingvalue of R, G, or B. and X_(L) is the backlight brightness value at thatpixel of R_(L), G_(L), or B_(L). Thus, a given RGB to RGBW gamut mappingalgorithm may have the input value R/R_(L), G/G_(L), B/B_(L). Those ofskill in the art will appreciate that the use of X/X_(L) function 136allows for an “off-the-shelf” GMA function to be utilized (e.g., any ofthe gamut mapping functions disclosed in the above-referencedapplications), without a modification needed to accommodate the lightcontributions of the light emitters in backlight array 120.

Note that backlight control methods and techniques described herein mayalso be combined with frame or field blanking for some period so as toreduce or eliminate the motion artifact known as “jutter”.

Handling Out-of-Gamut Colors with Expanded Peak Function

When Peak Function 110 uses an algorithm whose output values for a givenlight emitter are local peak values of the input image data, (e.g.,computed in an area bounded by the neighboring light emitters of thesame color) setting the light emitters to these local peak values maycause bright (relative to the local peak) saturated image colors to be“out-of-gamut” (OOG). This, in turn, could require the backlight lightemitters to be set at a higher brightness to allow these bright imagecolors to be reached.

The Peak Function may be designed to account for setting light emittervalues that are different from those found from a simple local peakfunction, and that accommodate what could otherwise be out-of-gamutimage colors. The block diagram in FIG. 1B illustrates expanded PeakFunction 1100, which could be implemented to substitute for PeakFunction 110 of FIG. 1A. Peak Survey function 110 (which operates thesame as Peak Function 110 in FIG. 1A) surveys the linear input image RGBvalues of each pixel to find the peak value for a light emitter withineach of the light emitter Point Spread Function areas.

To determine if these light emitter values will cause some of the inputimage colors to be out-of-gamut, a gamut mapping function is performedwith the output light emitter values produced by Peak Survey 110. Thus,expanded Peak Function 1100 includes additional functionality that isduplicative of other functions previously described in display system100 to identify and accommodate input color values that would beout-of-gamut with light emitter settings determined using a local peakfunction.

With continued reference to FIG. 1B, the light emitter values outputfrom Peak Survey 110 are input to Backlight Interpolation function 130to produce the R_(L)G_(L)B_(L) values, as described above. Thenormalization of the input image RGB values and the R_(L)G_(L)B_(L)values, as previously described, is then performed in box 135. Then thenormalized values are input to gamut mapping function RGB(W) GMAfunction 1150. However, the output W and L values that are otherwisegenerated in the standard RGBW GMA function are not needed in this case,since only the RGB values from RGB(W) GMA function 1150 are subject tobeing out-of-gamut. The output RGB values from RGB(W) GMA 1150 are thensurveyed by the OOG Peak Survey 1160 to find the maximum out-of-gamutvalue within each light emitter's Point Spread Function area. Themaximum out-of-gamut value is multiplied, possibly with a suitablescaling factor, with the original light emitter values produced by PeakSurvey 1110, in Peak Adjustment function 1170, to increase the values ofthe light emitters such that fewer out-of-gamut colors occur.

Second Embodiment of a Display System Multi-Primary Color BacklightArray with Multi-Primary Display

FIG. 2A is a block diagram of a second exemplary display system 200having a spatial light modulator panel 260 for producing images, whichis labeled as a liquid crystal display (LCD) panel in FIG. 2A. Panel 260is a multi-primary subpixelated display panel and is shown in FIG. 2A ascomprising five colors designated as red-green-blue-cyan-white (RGBCW).Subpixel repeating group 902 of FIG. 9 is an example of a subpixelrepeating group suitable for use on panel 260. Exemplary display system200 also includes an array of light emitting sources 220 used as abacklight for panel 260. Array 220 is comprised of light emitters indifferent colors, each of which is independently addressable underelectronic control such that the control of each individual color may becompletely separated from control of each of the other colors in array220. FIG. 2A shows the array of light emitting sources 220 comprisingLEDs but it is understood that other types of light emitters, such asthose enumerated above with respect to the display system illustrated inFIG. 1A, that are capable of being independently addressable andcontrolled are also suitable for use in the embodiment of the displaysystem illustrated in FIG. 2A.

In FIG. 2A, array 220 is labeled as having light emitters in fourcolors, RGBC, and in particular, in primary colors corresponding to theprimary colors used in the subpixel repeating group of panel 260.Display system 200 illustrates a display system in which backlight array220 has light emitters in N saturated primary colors (referred to as“s.primary”) that match the N saturated primary colors of the subpixelrepeating group used in display panel 260, where the W primary isconsidered to be a non-saturated primary. Note that, when the displaydoes not include a W primary, the saturated primary colors of thedisplay may be a one-for-one match with the saturated primary colors ofthe light emitters of array 220. However, as will be explained in moredetail below, there may be significant benefits in image quality and inthe dynamic range of the colors achieved in output images from using thebacklight control techniques described herein in conjunction with adisplay system having a W primary.

Input Image Data Path

In display system 200, input image RGB data is subject to gamut mappingfor both control of the N-s.primary backlight array and for subpixelrendering to produce the output color image in the gamut of N-primarydisplay panel 260. To operate on linear data, the incoming R*G*B* data,which by common convention is non-linearly, or gamma quantized, isconverted by the Gamma (γ) Look-Up-Table (LUT) 205 to higher bit depthlinear RGB values.

The RGB data output from input gamma function 205 proceeds toN-s.primary GMA function 207 which maps the RGB input image data to thecolor gamut of the N saturated primaries of backlight array 220. GMAfunction 207 may be any of the gamut mapping algorithms that map inputRGB to N saturated primary colors as disclosed in the above referencedcommonly-owned patent applications, or otherwise known in the art or yetto be discovered. For example, PCT Application PCT/US 06/12766 (entitled“Systems and Methods for Implementing Low-Cost Gamut Mapping Algorithms,hereafter the “PCT '766 application”) teaches how to convert threevalued color input signals into four valued color signals. This methodmay be used in GMA function 207 for conversion of RGB input image datainto a four primary color gamut of backlight array 220 (FIG. 2A) suchas, for example, an RGBC backlight array.

GMA function 207 may also benefit from using metamer selectiontechniques as described in U.S. patent application Ser. No. 11/278,675,entitled “Systems and Methods for Implementing Improved Gamut MappingAlgorithms.” When four or more non-coincident primary colors are used ina multi-primary display, there are often multiple combinations of valuesfor the primaries that may give the same color value. A metamer on asubpixelated display is a combination (or a set) of at least two groupsof colored subpixels such that there exist signals that, when applied toeach such group, yields a desired color that is perceived by the humanvision system. Substituting a metamer for a given color may reduce orequalize the peak values of the component colors in the output Nsaturated primary color space of the light emitters. This, in turn, mayresult in one or more of the light emitters being optimally dimmed toallow for optimal requantization of the output image values andreduction of backlight power.

The output color signals of GMA function 207 (specified in the colorspace of the N saturated primary colors of the light emitters inbacklight array 220) is processed by Peak Function 210 to generate thevalues of the light emitters for array 220. In effect, as describedabove, Peak Function 210 generates a low resolution color image forarray 220, specified in the N s.primary colors of backlight array 220.

The low resolution color image output from Peak Function 210 is alsoused by Backlight Interpolation module 230 to calculate the color andbrightness of the backlight at each input location. Alternatively,module 230 may calculate the color and brightness at every subpixellocation of panel 260. Then, prior to processing by gamut mappingoperation 240, the input image RGB values, as mapped to the N s.primarycolors of backlight array 220, and the low resolution image output byBacklight Interpolation module 230 are normalized, in module 235. In thecontext of a multi-primary display system having RGBCW primary colorswith a backlight array having light emitters in RGBC primary colors,normalization function 235 computes the ratio of RGBC input colors toR_(L)G_(L)B_(L)CL values, effectively making the backlight bright whiteto gamut mapping function 240. As noted above, using normalizationfunction 235 permits display system 200 to utilize an “off-the-shelf”gamut mapping function, without requiring any special or costlymodifications.

Second gamut mapping function 240 converts the normalized input imagedata, as specified in the color space of the N s.primary colors of array120 (e.g., RGBC color data) to the primary color system of display panel260 (e.g., RGBCW.) GMA function 240 may also calculate luminance, L, aswell as the primary color values, for use in SPR function 250, asdescribed in US Patent Application Publication 2005/0225563 and in theMetamer Filtering application. The output image data from SPR 250function is sent to output inverse gamma (γ⁻¹) Look-Up-Table (LUT) 215to compensate for the non-linear response of the display.

Operation of Gamut Mapping Functions

As noted above, GMA function 207, which maps the input RGB image data tothe color space of the saturated primary colors of the backlight array,may use techniques disclosed in the PCT '766 application for conversionof RGB input image data into a four primary color gamut of backlightarray 220 (FIG. 2A) such as, for example, an RGBC backlight array GMAfunctions 240 (FIG. 2A) and 2160 (FIG. 2B) may use procedures similar tothe techniques disclosed in the PCT '766 application, but expanded asshown below, to convert the four valued (RGBC) color signal produced byGMA function 207 to the RGBCW signal needed by display panel 260. Forease of reference, the discussion below will relate specifically to anRGBC backlight array and an RGBCW display panel, but it is understoodthat the methods and equations may be adapted to operate when thebacklight array and display panel have the same number of saturatedprimaries (e.g., RGBC to RGBCW or RGBY (Y=yellow) to RGBYW, or otherprimary color combinations,) or when the display panel has one moreprimary than the n.saturated primaries of the backlight array.

In the process of developing GMA function 207, a 4×3 matrix iscalculated from the luminosity and chromaticity of the RGBC backlightarray. This matrix converts RGBC values to CIE XYZ and can be calculatedusing methods well known in the literature. This matrix is used inequations like the following:

$\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {\begin{pmatrix}{m\; 00} & {m\; 01} & {m\; 02} & {m\; 03} \\{m\; 10} & {m\; 11} & {m\; 12} & {m\; 13} \\{m\; 20} & {m\; 21} & {m\; 22} & {m\; 23}\end{pmatrix} \cdot \begin{pmatrix}{Rc} \\{Gc} \\{Bc} \\{Cc}\end{pmatrix}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Similarly, a 5×3 matrix can be calculated to convert RGBCW values to CIEXYZ using the same methods. This matrix is used in equations like thefollowing:

$\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {\begin{pmatrix}{n\; 00} & {n\; 01} & {n\; 02} & {n\; 03} & {n\; 04} \\{n\; 10} & {n\; 11} & {n\; 12} & {n\; 13} & {n\; 14} \\{n\; 20} & {n\; 21} & {n\; 22} & {n\; 23} & {n\; 24}\end{pmatrix} \cdot \begin{pmatrix}{Rw} \\{Gw} \\{Bw} \\{Cw} \\{Ww}\end{pmatrix}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

For a single color, these two equations can be set equal to each other,giving:

$\begin{matrix}{{\begin{pmatrix}{m\; 00} & {m\; 01} & {m\; 02} & {m\; 03} \\{m\; 10} & {m\; 11} & {m\; 12} & {m\; 13} \\{m\; 20} & {m\; 21} & {m\; 22} & {m\; 23}\end{pmatrix} \cdot \begin{pmatrix}{Rc} \\{Gc} \\{Bc} \\{Cc}\end{pmatrix}} = {\begin{pmatrix}{n\; 00} & {n\; 01} & {n\; 02} & {n\; 03} & {n\; 04} \\{n\; 10} & {n\; 11} & {n\; 12} & {n\; 13} & {n\; 14} \\{n\; 20} & {n\; 21} & {n\; 22} & {n\; 23} & {n\; 24}\end{pmatrix} \cdot \begin{pmatrix}{Rw} \\{Gw} \\{Bw} \\{Cw} \\{Ww}\end{pmatrix}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Equation 3 cannot be directly solved for [Rw,Gw,Bw,Cw,Ww] given a set ofthe [Rc,Gc,Bc,Cc] values because none of the matrices are square.However, the inability to solve the equation symbolically does not meanthere is no solution. To the contrary, there are many solutions and onlyone may suffice to produce a reasonable display.

The above-referenced PCT '766 application teaches that equations with4×3 matrices may be solved by setting one of the unknowns to a“reasonable” constant. This converts the matrix to a square matrix,which allows for solving for the remaining variables. In Equation 3, thecyan (Cw) and white (Ww) values can both be declared constants and then“factored” out of the matrix. For example, in displays with a white(clear) subpixel it has been found reasonable to set the Ww value to theluminosity of the input value. In a similar manner, the Cw value may beset to the input Cc value. With these two variables converted toconstants, the equation can be changed to the following:

$\begin{matrix}{{\begin{pmatrix}{m\; 00} & {m\; 01} & {m\; 02} & {m\; 03} \\{m\; 10} & {m\; 11} & {m\; 12} & {m\; 13} \\{m\; 20} & {m\; 21} & {m\; 22} & {m\; 23}\end{pmatrix} \cdot \begin{pmatrix}{Rc} \\{Gc} \\{Bc} \\{Cc}\end{pmatrix}} = {{\begin{pmatrix}{n\; 00} & {n\; 01} & {n\; 02} \\{n\; 10} & {n\; 11} & {n\; 12} \\{n\; 20} & {n\; 21} & {n\; 22}\end{pmatrix} \cdot \begin{pmatrix}{Rw} \\{Gw} \\{Bw}\end{pmatrix}} + {\begin{pmatrix}{n\; 03} & {n\; 04} \\{n\; 13} & {n\; 14} \\{n\; 23} & {n\; 24}\end{pmatrix} \cdot \begin{pmatrix}{Cw} \\{Ww}\end{pmatrix}}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Equation 4 can now be solved for the remaining variables, producing thefollowing:

$\begin{matrix}{\begin{pmatrix}{Rw} \\{Gw} \\{Bw}\end{pmatrix} = {\begin{pmatrix}{n\; 00} & {n\; 01} & {n\; 02} \\{n\; 10} & {n\; 11} & {n\; 12} \\{n\; 20} & {n\; 21} & {n\; 22}\end{pmatrix}^{- 1} \cdot {\quad\left\lbrack {{\begin{pmatrix}{m\; 00} & {m\; 01} & {m\; 02} & {m\; 03} \\{m\; 10} & {m\; 11} & {m\; 12} & {m\; 13} \\{m\; 20} & {m\; 21} & {m\; 22} & {m\; 23}\end{pmatrix} \cdot \begin{pmatrix}{Rc} \\{Gc} \\{Bc} \\{Cc}\end{pmatrix}} - {\begin{pmatrix}{n\; 03} & {n\; 04} \\{n\; 13} & {n\; 14} \\{n\; 23} & {n\; 24}\end{pmatrix} \cdot \begin{pmatrix}{Cw} \\{Ww}\end{pmatrix}}} \right\rbrack}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Equation 5 can be simplified to the following:

$\begin{matrix}{\begin{pmatrix}{Rw} \\{Gw} \\{Bw}\end{pmatrix} = {\begin{pmatrix}{a\; 00} & {a\; 01} & {b\; 02} \\{a\; 10} & {a\; 11} & {b\; 12} \\{a\; 20} & {a\; 22} & {b\; 23}\end{pmatrix} \cdot \begin{pmatrix}{Cw} \\{Ww} \\1\end{pmatrix}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

where the “a” coefficients are calculated using Equation 2 (the 5×3conversion matrix), which can be pre-calculated once in advance. The “b”coefficients are calculated using both matrices and the input[Rc,Gc,Bc,Cc] values, which change on every input pixel. Note thatcareful selection of the primary colors in the backlight and theoverlying LCD display can greatly reduce the complexity of thesecalculations. Now the remaining [Rw,Gw,Bw] values can be calculated.

The resulting color may still be out-of-gamut in the RGBCW color space.Out-of-gamut colors can be resolved using any one or more of severaltechniques. Some colors may be brought back into gamut by using themetamer selection techniques as described in U.S. patent applicationSer. No. 11/278,675, entitled “Systems and Methods for ImplementingImproved Gamut Mapping Algorithms.” Depending on the shapes of the gamutrepresenting the backlight array primary colors and the gamut of thedisplay, there may still be some colors that can never fit into thefinal gamut. These colors must be clamped or scaled using techniquessuch as those disclosed in the '341, '352 and '344 applications and the'219 patent incorporated by reference above, or using other gamutclamping techniques from the literature.

The backlight control methods and techniques discussed herein may alsobe implemented in display systems in which the display panel has fewersaturated primary colors than saturated primaries of the backlight, orin which the display panel does not share primary colors with thebacklight. In these case, some other combination of GMA algorithms maybe preferred over using the two stage GMA functions illustrated in FIG.2A. For example, GMA function 240 may do its conversion directly fromthe RGB input color image data values produced by input gamma LUT 205.The GMA function may use algorithms based on techniques disclosed inseveral ones of the above-referenced patent applications, such as thosedisclosed in the '341, '352 and '344 applications and the '219 patentincorporated by reference above, or based on other gamut mappingalgorithms available in the literature.

Handling Out-of-Gamut Colors with Expanded Peak Function

When Peak Function 210 uses an algorithm whose output values for a givenlight emitter are local peak values of the input image data, (e.g.,computed in an area bounded by the neighboring light emitters of thesame color) setting the light emitters to these local peak values maycause bright (relative to the local peak) saturated image colors to be“out-of-gamut” (OOG). This, in turn, could require the backlight lightemitters to be set at a higher brightness to allow these bright imagecolors to be reached.

The Peak Function may be designed to account for setting light emittervalues that are different from those found from a simple local peakfunction, and that accommodate what could otherwise be out-of-gamutimage colors. The block diagram in FIG. 2B illustrates expanded PeakFunction 2100, which could be implemented to substitute for PeakFunction 210 of FIG. 2A. Peak Function 2100 will be described in termsof a display system having RGBCW primary colors and a backlight arrayhaving RGBC colored light emitters, but it is understood that theoperation of Peak Function 2100 may be modified to accommodate othermulti-primary display systems having a different set of N primarycolors.

Peak Survey function 210, which operates the same as Peak Function 210of FIG. 2A, surveys the linear input image RGBC values of each pixel tofind the peak value for a light emitter within each of the light emitterPoint Spread Function areas. To determine if these light emitter valueswill cause some of the input image colors to be out-of-gamut, a gamutmapping function is performed with the output light emitter valuesproduced by Peak Survey 2110 to identify and accommodate input colorvalues that would be out-of-gamut with light emitter settings determinedusing a local peak function.

With continued reference to FIG. 2B, the light emitter values outputfrom Peak Survey 2110 are input to Backlight Interpolation function 2130to produce the R_(L)G_(L)B_(L)CL values. The normalized input image RGBCvalues and the R_(L)G_(L)B_(L)CL values produced in box 2135 are inputto gamut mapping function RGBC(W) GMA function 2140. However, the outputW values that are otherwise generated in the standard RGBCW GMA functionare not needed in this case, since only the RGBC values from RGBC(W) GMAfunction 2140 are subject to being out-of-gamut. The output RGBC valuesfrom RGBC(W) GMA function 2140 are then surveyed by the OOG Peak Survey2160 to find the maximum out-of-gamut value within each light emitter'sPoint Spread Function area. The maximum out-of-gamut value ismultiplied, possibly with a suitable scaling factor, with the originallight emitter values produced by Peak Survey 2110, in Peak Adjustmentfunction 2170, to increase the values of the light emitters such thatfewer out-of-gamut colors occur.

Operation of the Backlight to Improve Quality of Displayed Images

In one embodiment of the operation of the backlight according to thetechniques described above, the chromaticity of the backlighting of thedisplay panel is dynamically controlled as a function of one or morecharacteristics of the colors in the image to be displayed on the panel.

Adjusting Light from Backlight to Image Color Temperature

One such characteristic of the colors in an image is referred to as thecolor temperature of the image, which may be defined as an average imagecolor and luminance. Using the backlight control techniques describedabove, the backlight array of the display may be controlled to emitlight as a function of the color temperature of the image beingdisplayed. For example, an image showing a sunset may include highnumbers of red and blue colors, but a low number of green colors. Incontrast, an image showing a moonlit scene may be predominantly silverywhite in color, having predominantly blue colors, but with few or noother colors. Using the backlight control techniques described above,the color temperature of the image may be determined by the displaycontroller, which in turn may control the color temperature of thebacklight array so that each scene may be rendered using its respectiveaverage color and luminance. Dynamically rendering an image in thismanner will also allow the limited dynamic range and quantization of thedisplay panel to be used to its fullest extent within the averageluminance and color of the image, which in turn reduces quantizationerror. Note that the aforementioned examples of images may occur as partof a sequence of images, or scenes, that are to be rapidly displayed,such as those that occur in the frames of a video or movie. The displaysystems described above that are implemented with the backlight controltechniques described herein may control the backlight color temperaturefrom frame to frame, as the image temperature changes from scene toscene.

In addition, when the backlight is an array of multicolor light emittershaving a lower resolution than the resolution of the display panel, suchas an LED display, color temperature adjustments may be made acrossdifferent regions of the panel, allowing specific parts of an image tobe illuminated by different color temperatures from the backlight array,and thus providing for high simultaneous dynamic range in both luminanceand chrominance within a single scene.

Controlling Light from Backlight to Alter the W Display Primary

Related to, but distinct from, using the color temperature of an imageto control the light emitting from the backlight is to use the backlightcontrol techniques described above to cause the backlight array to emitlight as a function of the predominant color in an image, in order toproduce a displayed image having higher luminance or higher color puritythan would otherwise be achieved using a uniform white backlight for thesubpixel repeating group used by the display panel.

First, a specific example will describe the problem. An image showing ascene in a photo-development dark room is typically lit only in red.With a conventional white backlight, only the red subpixels in thesubpixel repeating group of the display panel would be called upon bythe subpixel rendering (SPR) operation to render the luminanceinformation of the scene. In a standard RGB stripe display, only one ofthe three subpixels in the RGB subpixel repeating group will provide theluminance information for the image. Similarly, with reference to RGBWsubpixel repeating group 620 of FIG. 6, only one in three subpixels willprovide the luminance information for the image, and when a displaypanel utilizes RGBW subpixel repeating group 320 of FIG. 3, only one infour subpixels will provide the luminance information. In multi-primarydisplays such as those using the subpixel repeating groups shown in FIG.7, 9, or 24, the luminance information in the red image would only useone in six subpixels in subpixel repeating group 701 (FIG. 7), one ofsix subpixel in subpixel repeat group 2402 (FIG. 24), and only one ofeight subpixels in subpixel repeating group 902 (FIG. 9).

In a display system such as display system 100 of FIG. 1A and displaysystem 200 of FIG. 2A that implements the backlight control techniquesdiscussed above, the light emitted from the backlight array may becontrolled to be pure red light, allowing the normally white (clear)subpixels 304 of an RGBW display layout 320 (FIG. 3) to contribute tothe scene rendering, for a total of four of the eight subpixels (or twoout of four) providing the luminance information for the predominantlyred dark room image. A similar improvement is achieved with multiprimarysubpixel repeating group 902 of FIG. 9, which, without the use of thebacklight control techniques discussed herein, as noted above, providesfor only one of eight subpixels in subpixel repeating group 902 toprovide the luminance information for a predominantly red image. Withthe use of the backlight control techniques discussed herein, pure redimages would also use the more numerous white (clear) subpixels 904,adding four subpixels in addition to red subpixel 906, for a total offive subpixels out of eight in a display panel utilizing subpixelrepeating group 902. Moreover, the increased utilization of the clearsubpixels for highly saturated colors increases the brightness range ofthose colors. In addition, the red color would be truly red, since therewould be no color bleed from the other colors, thus increasing the colorpurity and gamut of the display.

FIG. 13 further illustrates the use of a backlight-controlled primarycolor in multi-primary display panel 1300A substantially comprisingsubpixel repeating group 1302. Subpixel repeating group 1302, which is avariation of subpixel repeating group 902 of FIG. 9, substantiallycomprises red 1304, green 1308, cyan 1320 and blue 1312 subpixels withmajority white subpixels 1306 interspersed. The minority saturatedsubpixels are each placed on a hexagonal grid. See, for example, cyansubpixels 1322, 1324, 1326, 1328, 1330 and 1332 surrounding cyansubpixel 1340.

In US Published Patent Application 2005/0225575, entitled “NovelSubpixel Layouts and Arrangements for High Brightness Displays,” varioussubpixel repeating groups including white subpixels are disclosed. The'575 application notes that the backlight color temperature may beadjusted to have more magenta (i.e., red and blue) energy than that forthe typical RGB stripe display to give a balanced white. The backlightcontrol techniques discussed herein, however, may actually control thecolor of the light emitters in the backlight so as to provide additionalprimary color subpixels. In the red image example described above, onlyone (the red) of the eight subpixels provides the luminance informationfor a predominantly red image when display panel 1300A is lit by aconventional white backlight. The other pixels, including the majoritywhite 1306 subpixels are shown in black, indicating that they are “off.”

With continued reference to FIG. 13, display panel 1300B illustrates howthe backlight control methods and techniques discussed above affect thedisplay of an exemplary predominantly red image by facilitating the useof a white (clear) subpixel in a display having a multi-primary subpixelrepeating group to function as an instance of a primary color, referredto herein as backlight-controlled (BC) primary color. Pure red imagesare displayed using the more numerous white (clear) subpixels 1306,adding four subpixels in addition to red subpixel 1304, for a total offive subpixels out of eight in display panel 1300B utilizing subpixelrepeating group 1302. The majority white subpixels 1306 in panel 1300Bnow transmit the red color (as indicated by their vertical hatching)from the underlying light emitter(s), as determined using peak function110 or 1100 in FIGS. 1A, 1B, or peak function 210 or 2100 in FIG. 2A or2B, respectively, and backlight interpolation function 130 (FIG. 1A) or230 (FIG. 2A), and from the remaining display functions (i.e., the GMA,SPR and output gamma functions) in the data path of the display.

The arrangement of subpixels 2400 of FIG. 24 shares the property foundin FIG. 9, of having a white (clear) subpixels 2406 on a square grid andfour saturated primaries, red 2404, green 2408, blue 2412, and cyan (oremerald green) 2420. As with other layouts disclosed herein, thisarrangement may use the commercially commonly available one-to-three(1:3) aspect ratio subpixel structure usually associated with theconventional RGB Stripe subpixel arrangement well known in the art. Ofcourse, other aspect ratios are possible with this subpixel repeatinggroup. It also may be able to use the “diamond” (and other shapedfilters) subpixel rendering filters disclosed in the '612, '724 and '563applications. It also may also use the metamer filtering techniquesdescribed in the Metamer Filtering application

Controlling Light from the Backlight Array to Alter Other Primary Colorsof the Display

The backlight control techniques described above may also be used toaffect how other ones of the primary colors of the display, in additionto, or in place of, the white subpixel, participate in increasing thesubpixel rendered image quality. For example, certain ones of thecolored light emitters in the backlight array that are disposed behindcertain ones of the colored subpixels of a particular subpixel repeatinggroup in a region of the display panel may be turned off to affect thecolor ultimately produced by the subpixel repeating group in that regionConsider, for example, a multi-primary display system having a displaypanel with subpixel repeating group 701 of FIG. 7, which has six primarycolors. If a bright saturated yellow region of an image is to bedisplayed using a conventional uncontrolled backlight, only three of thesix subpixels, the red 706, green 708, and yellow 711 subpixels would beturned on to produce the yellow image region. When a backlight arraycontrolled according to the techniques and methods discussed herein isused, the blue light emitters disposed behind the yellow image regionare turned off. This would allow the addition of two more of the sixsubpixels to be turned on: the magenta subpixel 709, which passes bothred and blue light, and wide passband cyan subpixel 707, which passesboth blue and green portions of the backlight spectrum, for a total offive out of six subpixels. Turning off the blue light emitters in theyellow image region effectively causes additional reconstruction pointsto be added for the subpixel rendering of the highly saturated color.

In effect, the backlight controller dims the light emitter of a givencolor so that the overlying display panel subpixel of that same colormay be set to maximum transmission for the highest pixel value in thearea of the Point Spread Function (PSF) of the light emitter. Thisallows surrounding subpixels of that same color that may be of lowerbrightness to be adjusted with more grey levels available on the displaypanel, in turn decreasing the quantization error Dimming certain ones ofthe light emitters in an image region also may increase the color gamutslightly because these dimmed light emitters will not be producing lightthat may potentially leak through nearby color filters, and may alsoincrease the contrast of the displayed image because these dimmed lightemitters will not be producing light that may potentially leak throughthe same filtered subpixel in the off state. Dimming the light emittersin the backlight to achieve the improved image quality also reducespower drain and extends battery life, a substantial benefit for batterypowered devices.

The ability to turn off selected ones of the light emitters in thebacklight array in order to improve the display of highly saturatedcolors may be used in conjunction with a multi-primary subpixelrepeating group having a white (clear) subpixel, in which the backlightcontrol is used to enable the white subpixel to become abacklight-controlled primary color. In the example of the predominantlyred darkroom image described above, the example presumed that the entireimage was predominantly red. Consider an image (e.g., an imagined moviescene) in which the illumination is pure red in a restricted region ofthe image, such as in a photographic darkroom viewed through an opendoor, or a ship's bridge under red emergency battle lighting viewedthrough a window, where the illumination in remainder of the image maybe considerably brighter, and the colors in the remainder of the imageare consequently less saturated. When this type of image is displayed ona multi-primary display using a conventional backlight, only the redsubpixels would be available to reconstruct the red illuminated imageregion. This reduces the Modulation Transfer Function Limit (MTFL) to bethe Nyquist Limit of the red subpixel which, in turn, may severely limitimage resolution in this image region.

Several of the above-referenced patent applications discuss allowingcross-luminance modulation of the other colored subpixels to solve thisimage resolution problem. That solution could cause some desaturation inareas of high spatial frequency detail. Further, for very highbrightness, highly saturated color image regions such as in the imaginedmovie scene, a bright, highly saturated color either must be clipped,clamped, or compressed to black, or must be clipped, clamped, orcompressed to luminance, in order to darken or desaturate all of theout-of-gamut colors. Each of these options is less than ideal since theymay lead to problems caused by simultaneous luminance contrast of darkersaturated color regions compared to a brighter desaturated image region.

The ability to individually control the light emitters in differentimage regions permits the backlight or display controller to turn offall but the desired light emitters in the bright saturated image regionwhile adjusting the light emitters in the other image regions as needed,thereby permitting the white (clear) subpixels join with the subpixelsof the given bright saturated color to keep both the resolution and thebrightness high without desaturating or clamping the colors of theimage. The white subpixel allows more of the saturated color to passthrough the LCD increasing the overall brightness and color gamut hullvolume

Resolution and Colors of Light Emitters in the Backlight Array

As noted above, in some embodiments of the display systems describedherein, it may be advantageous to require that the multi-primary colorfilters of the display panel match, or map, on a one-to-one basis tolight emitters in the backlight array. However, this is not arequirement in all display system embodiments encompassed by the scopeof the appended claims. That is to say, the light emitters for Nsaturated primary colors in the backlight need not be mapped to Nsaturated primary colors in the color filters of the display panel.

In fact, the controllable backlight array may include light emitters inany N colors, including those colors that are not typically found inbacklight arrays, such as deep-red, cyan (emerald), and violet. Forexample, in display systems having a backlight array that is itself acolor display having a lower resolution than the display panel thebacklight is illuminating, it may be desirable to use light emitters inthe backlight emitting colored light in more colors than, or differentcolors from, the primary colors that occur in the display panelilluminated by the backlight. For example, a “green” light emitter mayhave a peak wavelength of 530 nm, while a “cyan” light emitter may havea peak at 505 nm. It may be possible to pass both of these wavelengthsthrough a single color filter that spans both wavelengths. When asaturated, green to red color is needed in an image region, the greenlight emitter disposed in the backlight array behind that image regionis turned on; when a saturated cyan to blue color is needed in the imageregion, the cyan light emitter is turned on. When a white color isneeded in an image region, one or both of the cyan and green lightemitters may be turned on. Using the controlled backlight array in thismanner permits the display panel to be configured with a subpixelrepeating group having fewer different primary colors.

Other ranges of colors may be treated similarly. For example, in theblue region, the eye is most sensitive to 450 nm. This is good for highefficiency but light emitters in the deep violet range may also be used.The deeper violet light emitter near 400 nm has low visual efficiency,but provides for a greater color gamut in the line-of-purples where thehuman eye has greater color differentiation ability. When displaying animage region with deep violent colors, the 450 nm blue light emitter maybe turned off and the 400 nm deeper violet light emitter may be turnedon in that image region.

In the range of red colors, the human eye is less and less sensitive tothe light as the wavelength increases. To produce an image region havinga reasonably deep red with reasonable visual efficiency using thecontrolled backlight array, a 610 nm light emitter may be used. However,the 610 nm light emitter would not necessarily improve deeper red colorperception out to 700 nm. To improve color perception in this red range,the controlled backlight array may include a light emitter in the 700 nmrange. This longer wavelength light emitter may be turned on whenrequired, perhaps when along the deep line-of-purples, in concert withthe deeper violet light emitter described above, while turning off the610 nm light emitter. When the image region requires less saturatedcolors, the less saturated light emitters at 610 nm and 450 nm may beused to increase the backlight efficiency.

The choice of colors for the light emitters included in the backlightarray is not necessarily determined by the primary colors of thesubpixel repeating group comprising the display panel. Nor do theprimary colors of the subpixel repeating group comprising the displaypanel determine the choice of colors for the light emitters included inthe backlight array. Those of skill in the art will appreciate that theflexibility permitted by the backlight control techniques describedabove allow for configuring the colors and arrangement of the lightemitters in the backlight array to accommodate display systems havingdisplay panels of any one of the subpixel repeating groups illustratedin the Figures herein, or those subpixel repeating groups described inthe above-referenced patent applications, as well as the conventionalRGB stripe subpixel repeating group. Those of skill in the art willfurther appreciate that the configuration of the colors and arrangementof the light emitters in the backlight array may be designed tocomplement or match a particular subpixel repeating group. Variousexamples described herein show how design choices may be made.

A Display System Embodiment Having a Single White (Clear) Primary with aControlled Backlight Array

The above discussion describes various choices that can be made for thecolors of the light emitters in display systems having a backlight arraythat is itself a color display having a lower resolution than thedisplay panel the backlight array is illuminating. However, in somedisplay system embodiments, the resolution of the backlight array may behigh enough so that it is unlikely that one would need to show bothgreen to red colors and cyan to blue colors in the same small imagearea. That is, the backlight array of light emitters is of high enoughresolution that it is not likely or perhaps even possible to perceive,due to the limits of the human eye, a color juxtaposition that requireshigher color resolution than the resolution of the backlight display. Inthis particular case of providing a wider color gamut by choosingcertain light emitters for the backlight array, it may be possible toprovide a display panel that has only one color subpixel; that is, thedisplay panel has as its “subpixel repeating group” a pure transparent,unfiltered white (clear) subpixel. In that case, an array of onlytransparent subpixels would then provide all of the high resolutionluminance modulation for the displayed image while the backlight array(display) of N primary color light emitters provides all of the lowerresolution color.

Embodiment of Liquid Crystal Display System

FIG. 10 is a simplified (and not to scale) block diagram of a liquidcrystal display (LCD) system 1000 in which any one of the embodimentsdisclosed herein may be implemented. LCD 1000 includes liquid crystalmaterial 1012 disposed between glass substrates 1004 and 1008. Substrate1004 includes TFT array 1006 for addressing the individual pixelelements of LCD 1000. Substrate 1008 includes color filter 1010 on whichany one of the subpixel repeating groups illustrated in the figuresherein, and in the various ones of the co-owned patent applications, maybe disposed. LCD 1000 also includes backlight 1020 which includes anarray of light emitters as illustrated in FIGS. 4 and 5, includingvariations as described herein in the discussion accompanying thosefigures. Display controller 1040 processes the RGB image input colorvalues according to the functions described in FIG. 1A or 2A. The RGBinput image values are also input to backlight controller 1060 for usein setting the values of the light emitters in backlight 1020, accordingto the operation of the Peak Functions described in the variousembodiments of FIGS. 1A, 1B, 2A and 2B. Backlight controller 1060communicates with display controller 1040 in order to provide the valuesof the light emitters for use by Backlight Interpolation function 130 or230 in order to compute the low resolution image R_(L)G_(L)B_(L).

Alternative Out-of-Gamut Processing on Low Resolution Backlit DisplaySystems

With any display system comprising a low resolution, coloredbacklighting as described above in all of its variants (e.g. LEDbacklight, a 2-LCD configuration, or the like), there are opportunitiesto process image data in novel fashions that leverage the uniquecombination of such a system.

For one example, as noted above, after some process of adjusting thecolored backlight—for example, by adjusting the LED array values—therestill might be colors that are out of gamut. This might happen, forexample, at very high brightness when colors change hue within the pointspread function of the LEDs (or other low resolution backlightingsystems).

It may be possible to process the image data—to include possibly boththe backlight and the LCD subsystems—in a temporal or spatial-temporalfashion to bring the colors that are out of gamut back into a targetgamut space. Such a temporal/spatial-temporal processing may either takeplace on a global (e.g. on the entire image rendered upon the display)or local (e.g. within a subset region of the image rendered upon thescreen). As such, it may be possible to modulate the low resolutionbacklight over time at only a certain time and within a certain regionwhere such out of gamut conditions might exist within an image.

For example, one embodiment might proceed as follows: for any region(including the entire image) where there exists an out of gamutcondition in, for example, a first color (e.g. red), subtract theopposite colors from the first color (in the example, cyan or green andblue) color from the peak value of the backlight color until such out ofgamut color is back in gamut.

It is possible to group colors either by the primaries of the backlightor, alternatively, by their peak OOG conditions without regard to thebacklight primaries. In the second alternative, color fields would notnecessarily be pure colors. One example of such processing is now givento illustrate one embodiment and it will be appreciated that otherembodiments and variants thereof are contemplated under the scope of thepresent invention.

Assume an RGB LED backlight with a RGBW LCD layout. The RGBW LCDsubpixel repeating group may be any such group imagined, including onesdisclosed herein and any others (e.g. RGBW quad). For this embodiment,it suffices only that there be a white or clear subpixel or similar widebandpass filtered subpixel used within the subpixel layout of the LCD.The RGB LED backlight may be arrayed in any suitable fashion—e.g. in asquare, displaced or some other arrangement. In addition, it sufficesthat that the backlight meets some assumptions for its design. Forexample, one such assumption might be that, at any given point on thedisplay, it is possible to illuminate that point with a certain level ofwhite (or alternatively, any given color) light illumination, accordingto the point spread function of the individual LEDs and the geometricarrangement of the LEDs upon the backlight display. It will beappreciated that the techniques described herein for OOG methods andsystems as described in reference with RGB backlight with RGBW LCD maybe suitably generalized to N-primary colored backlight and M-coloredmultiprimary LCD displays—where N and M may or may not be equal to eachother and where even if N=M, then colored primaries are different in thebacklight and the LCD.

In this example, three fields (corresponding to the virtual primariesP1, P2, P3, as discussed below) may be used for those LEDs that might beout of gamut: P₁, P₂ and P₃. The values of the LEDs in each field may befound by a survey of the incoming RGB data (or other suitable dataformat) in reference to each LEDs point spread function. It should benoted that the final values of the LED brightness may also be adjustedfor field light integration. Thus, the total amount of light over thethree fields sums substantially to the total desired, and the averageequal substantially the Max desired. Stated otherwise:

Equation 8 P₁ field P₂ field P₃ field Sum (R₁ + R₂ + R₃)/3 = Max(R_(in))(G₁ + G₂ + G₃)/3 = Max(G_(in)) (B₁ + B₂ + B₃)/3 = Max(B_(in))

If a given pure color is to be created using only one field, and it isdesired to be proportionally as bright as the color made with threefields, then that single field may be three times as bright. If the LEDsare flashed, the heat build-up is approximately proportional to thebrightness of each flash and the flash rate, as is the power and thebrightness. Thus, flashing the LED at three times the brightness but onethird the rate provides approximately the same brightness but one thirdthe rate provides the same brightness and power requirements.

It will be appreciated by those skilled in the art that the prior artField Sequential Color (FSC) system may be used, in which the fields arepure color primaries defined by the colors of the LED primaries. Animprovement may be to set the maximum brightness of a given color LED inthe backlight to the brightest value required by the image data to bedisplayed on the LCD and adjust the LCD value by X/X_(L) to allow all ofthis light to pass through the LCD

Dynamic Virtual Primaries

Another improvement however, may be to use “virtual primaries” that maycover less than the full color gamut of the backlight within a givenregion of the LCD display in order to reduce the visibility of FSCartifacts known to occur with prior art FSC systems.

FIG. 16 shows a color gamut map 1600 (e.g. CIE '31) that bounds onepossible original input gamut map (1610)—in this example, a RGB gamut.This original gamut may be defined by the color points R, G and B of theconstituent RGB LEDs. Within RGB gamut 1610, a new gamut 1620 may bedefined and/or created that may be a subset of the input gamut map 1610.This new gamut 1620 is bounded by “virtual primaries” (e.g. 1630, 1640and 1650)—wherein the term “virtual primaries” describes the fact thatthe primary points 1630, 1640 and 1650 are not necessarily the exactphysical primaries defined by the LEDs (or other suitable lightemitters, e.g. OLED) themselves. Of course, some or all of the virtualprimaries optionally could be some or all of the primary points for someperiod of time. Instead, for example, each virtual primary point couldbe created by a mixture of illumination values of the R, G and B LEDs(or any set of colored light emitters in the backlight). Each of thesevirtual primary points exists for some unique space and timecoordinates. For example, virtual primary point 1630 could exist for oneframe of image data in time and may exist only for a limited number ofsubpixels within spatial portion of the display. To continue theexample, it may be possible for the display system to operate over threefields with virtual primaries 1630, 1640 and 1650 illuminating all orsome portion of the display image.

Alternatively, the virtual primary could exist over the entire imageframe or any spatial region in between the entire image frame or at oneor a few subpixels. Such granularity of space partitioning or regionsmay be possible because the backlight may be comprised of a lowresolution array of colored LEDs. Additionally, virtual primaries mayexist in time for an indefinite period of time, several or one frames,or even a portion of a frame—all depending upon the operating criteriaof the system.

As the present system may create virtual primaries for a wide variety ofspace and time conditions, it is worth mentioning some degenerate casesthat are possible given the flexibility of the present system. Onedegenerate case of the present system might be to assign the virtualprimaries to be precisely the actual (e.g. R, G and B LEDs or any otherset of actual light emitters) and have each such LED illuminationlasting for a frame and over the entire image. In such a case, thedisplay system could operate in a conventional “field sequential”fashion. Another degenerate case would be to assign only one virtualprimary point—white—by illuminating all three LEDs simultaneously overall fields. In such a case, the display system could operated in amanner described in the '737 publication noted above. These degeneratecases could be operated for any length of time desired by the system orthe user. However, given the dynamic nature of the present system,maximum flexibility is allowed the system and any assignment of virtualprimaries may be selected to optimize any number of operatingcriteria—as discussed further below.

It will be appreciated that any number (i.e. other than three) virtualprimaries may be selected and that the time slice in which theyilluminate any portion of the display is possible and possiblydesirable, depending on the operating criteria.

Selection and Choice of Virtual Primaries

Of the possible operating criteria which may be factored into theselection of virtual primaries, one listing might include: reducingflicker, reducing color breakup, maximizing power savings, increasingdynamic range, and reducing quantization error. Regardless of thecriteria sought to optimize, one embodiment might involve finding asuitable (and possibly the smallest, in one embodiment) chromaticitytriangle (or region other than triangular for more than three, or lessthan three, virtual primaries) that contains substantially all of thecolor values within the point spread function of a given LED or clusterof LEDs; identifying a new set of virtual primaries and then generatingFSC color values of each of these virtual primaries. This has the effectof creating a new GMA for each set of virtual primaries, possibly on thefly. Of course, these steps may be re-ordered in a fashion. In anotherembodiment, the virtual primaries could be selected—and on the basis ofthat selection—the chromaticity area may be found. The discussion belowwill described various embodiments of the present system that might beuseful in helping to optimize the systems performance under the set ofoperating criteria above.

For example, the following description is one embodiment of the presentsystem that may have as a goal to minimize flicker. Merely to aid in theexposition of the system, it will be assumed that the system is seekingto render a particular subset or area of an input image upon thedisplay. This area could be as large as the entire image frame itself oras small as a single subpixel within the point spread function of a fewbacklight LEDs—or any area or subset of the image in between the entireimage frame and a subpixel thereof. The choice of the image subset maybe selected by the user or the system itself.

To achieve this goal of reducing flicker, the system could seek thevalues for the LEDs in the image subset to have substantially theminimum luminance modulation—as the system operates as a dynamic FSCsystem. Flicker primarily occurs during the rendering of an image over anumber of fields when a low luminance field of color (i.e. blue) ispreceded or followed by a field of high luminance color (e.g. green).Many previous attempts to reduce flicker in FSC, projectors having colorwheels and like have been well documented in the literature. The presentsystem provides a different approach to reducing flicker.

Shown in FIG. 17, simplified for explanatory purposes only, anequilateral triangle 1700 is the original input color gamut (e.g. RGB inour example) and three virtual primaries, P₁, P₂ and P₃, are shown. Itwill be appreciated that the particular number of primaries of the inputgamut and number of virtual primaries might change with the actualnumber of backlight and LCD primaries and suitable changes to thepresent discussion could be effected to accommodate such differentsystems.

In one embodiment of the present system, the system may comprise: aspatial light modulator for displaying an output color image formed froman input signal comprising a set of color input values; the spatiallight modulator substantially comprising a set of individuallycontrollable transmissive elements; a plurality of individuallyaddressable colored light emitters disposed as a backlight to providelight for forming a color image on the spatial light modulator; eachlight emitter producing light in one of a plurality of primary colors;for a plurality of regions, said regions comprising a set of pointspread functions of a set of said light emitter, a first mappingoperation for selecting a set of virtual primaries that bound each colorinput value within each said region, said virtual primaries comprising aplurality of intensities of said plurality of said light emitters withinsaid set of point spread functions; field sequential control circuitryfor controlling the duration and illumination of said virtual primariesover a set of fields comprising an intermediate color signal formed bysaid light emitters within each said region to produce an intermediatecolor image onto said spatial light modulator; and circuitry forcontrolling said set of transmissive elements within each said region tomodulate said intermediate color image to produce said output colorimage. Each of these elements and subsystems will now be described withgreat detail below.

Finding Virtual Primaries

For any given color, C₁, inside the virtual primary gamut, there is avalue χ₁P₁, χ₂P₂ and χ₃P₃ that substantially equals the input RGB valuein appearance to the human vision system. As each virtual primary may bedecomposed into the original primary values, we have:

₁(R ₁ ,G ₁ ,B ₁)+₂(R ₂ ,G ₂ ,B ₂)+₃(R ₃ ,G ₃ ,B ₃)=RGB value for C₁  Equation 10

Restated as a matrix:

$\begin{pmatrix}R \\G \\B\end{pmatrix} = {\begin{pmatrix}{R\; 1} & {R\; 2} & {R\; 3} \\{G\; 1} & {G\; 2} & {G\; 3} \\{B\; 1} & {B\; 2} & {B\; 3}\end{pmatrix} \cdot \begin{pmatrix}{x\; 1} \\{x\; 2} \\{x\; 3}\end{pmatrix}}$

Then inverted to find the values:

$\begin{pmatrix}{x\; 1} \\{x\; 2} \\{x\; 3}\end{pmatrix} = {\begin{pmatrix}{R\; 1} & {R\; 2} & {R\; 3} \\{G\; 1} & {G\; 2} & {G\; 3} \\{B\; 1} & {B\; 2} & {B\; 3}\end{pmatrix}^{- 1} \cdot \begin{pmatrix}R \\G \\B\end{pmatrix}}$

Expanded:

$\begin{pmatrix}{x\; 1} \\{x\; 2} \\{x\; 3}\end{pmatrix} = \frac{\begin{pmatrix}\begin{matrix}{{{R \cdot G}\; {2 \cdot B}\; 3} - {{R \cdot G}\; {3 \cdot B}\; 2} - {{G \cdot R}\; {2 \cdot B}\; 3} + {{G \cdot R}\; {3 \cdot B}\; 2} +} \\{{{B \cdot R}\; {2 \cdot G}\; 3} - {{B \cdot R}\; {3 \cdot G}\; 2} - {{R \cdot G}\; {1 \cdot B}\; 3} + {{R \cdot B}\; {1 \cdot G}\; 3} +}\end{matrix} \\{{{G \cdot R}\; {1 \cdot B}\; 3} - {{G \cdot R}\; {3 \cdot B}\; 1} - {{B \cdot R}\; {1 \cdot G}\; 3} + {{B \cdot R}\; {3 \cdot G}\; 1}} \\{{{R \cdot G}\; {1 \cdot B}\; 2} - {{R \cdot B}\; {1 \cdot G}\; 2} - {{G \cdot R}\; {1 \cdot B}\; 2} + {{G \cdot R}\; {2 \cdot B}\; 1} +} \\{{{B \cdot R}\; {1 \cdot G}\; 2} - {{B \cdot R}\; {2 \cdot G}\; 1}}\end{pmatrix}}{\begin{pmatrix}{{R\; {1 \cdot G}\; {2 \cdot B}\; 3} - {R\; {1 \cdot B}\; {2 \cdot G}\; 3} - {R\; {2 \cdot G}\; {1 \cdot B}\; 3} +} \\{{R\; {2 \cdot B}\; {1 \cdot G}\; 3} + {R\; {3 \cdot G}\; {1 \cdot B}\; 2} - {R\; {3 \cdot B}\; {1 \cdot G}\; 2}}\end{pmatrix}}$

From Equation 10, it is possible to find expressions for χ₁, χ₂, and χ₃.Of course, there are many ways in which these values may bedetermined—including straight-forward matrix algebra manipulations asshown above. It will now be presented merely one possible embodiment fordetermining virtual primaries and a system (1800) utilizing it, as shownin FIG. 18.

System 1800 inputs image data into input gamma unit 1802. From there,image data may precede along either one or multiple data paths FIG. 18depicts a system with two data paths. In a first path, image data mayproceed somewhat as described above—along peak unit 1804, interpolationunit 1806, X/X_(L) unit 1808, GMA 1810, OOG peak unit 1812 to aup-sample unit 1814. From there, depending on the signal OOGP suppliedto Mux 1816, one of two data paths could be selected to drive backlight1822 and LCD 1824 via output gamma unit 1818 and a Field SequentialColor control unit 1820. OOGP is a signal that indicates whether or notthere were any OOG color values in the point spread function of an LED.If there were no such OOG color values, then the first data path isselected by Mux 1816. If there are, however, some OOG color values, thesecond data path is selected, employing some technique to prevent thecolors from going out of gamut. One such technique is the use of thesevirtual primaries.

A first step in calculating the virtual primaries could be to identifyall of the input sample colors that will lie inside the point spreadfunction of a single LED or cluster of LEDs if, for example, the LEDcolors are not coincident. The second data path could accomplish this byinputting data from input gamma unit 1802 to a bounding box unit 1830.Bounding box unit 1830 could find the these values and calculate amaximum and minimum value on each axis, for example max(R), min(R),max(B), min(B), max(G), min (G), etc. These limits describe a boundingbox that encloses all the colors inside the point spread function for asingle LED. FIG. 22 shows a diagram of this process. Points 2202represent all the input pixels that lie within the point spread functionof a single LED. The box 2204 shows two of the axes of the bounding boxthat result.

Next a formula for three planes may be found that enclose all the colorsinside the bounding box. These planes may be created by anchoring themat the origin at one point, at a corner of the bounding box at a secondpoint, and passing through the origin at 45 degrees to two of the axes.It may be visualized by considering each of the color planes for RG, GBand BR rotating towards the opposite axis (RG plane to B axis, GB to Rand BR to G) until they just touch one corner of the bounding box. Line2206 shows a representation of the RG plane, viewed on edge, rotatedtowards the blue axis until it touches the closest corner of boundingbox 2204.

Equation 11 ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\0 & 1 & {- 1} & 1 \\{\min (R)} & {\max (G)} & {\max (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the GB plane, and anouter corner of the bounding box. ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\{- 1} & 0 & 1 & 1 \\{\max (R)} & {\min (G)} & {\max (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the BR plane, and anouter corner of the bounding box. ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\1 & {- 1} & 0 & 1 \\{\max (R)} & {\max (G)} & {\min (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the RG plane, and anouter corner of the bounding box.

Each of these formulas in Equation 11 above describes a plane in colorspace that looks like a line in CIE xy space. If calculated as above,the lines in CIE xy space will be substantially parallel to thechromaticity triangle of the input data when close to the edges. Thismay be desirable if the bounding box lies near one of the inputprimaries. If the opposite corner of the bounding box is used to definethe three planes, the resulting triangle appears rotated about 60degrees to the triangle calculated by the method above. Line 2208 showsa representation of rotating the RG plane to the opposite corner ofbounding box 2204. This orientation may produce better results when thebounding box is closer to the center of the chromaticity triangle. Tocalculate the planes this way, it may be possible to use the followingformula:

Equations 12 ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\0 & 1 & {- 1} & 1 \\{\max (R)} & {\min (G)} & {\min (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the GB plane, and aninner corner of the bounding box. ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\{- 1} & 0 & 1 & 1 \\{\min (R)} & {\max (G)} & {\min (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the BR plane, and aninner corner of the bounding box. ${\begin{pmatrix}r & g & b & 1 \\0 & 0 & 0 & 1 \\1 & {- 1} & 0 & 1 \\{\min (R)} & {\min (G)} & {\max (B)} & 1\end{pmatrix}} = {0\quad}$ Determinant formula of a plane passingthrough the origin, a point on a 45 degree line on the RG plane, and aninner corner of the bounding box.

Alternatively, the bounding box unit could perform the above planeintersection calculations by surveying all of the input sample colorsthat will lie inside the point spread function of a single LED. Theangle to every input color in the point spread function may becalculated. The minimum (or alternatively, maximum) of these angles isused instead of the angle to the corner of the bounding box. Lines 2210and 2212 show how surveying all the points 2202 may result in a betterfit to the input colors 2202 than using the bounding box 2204 This inturn may select a smaller triangle and virtual primaries that are closertogether than a bounding box because a bounding box may enclose a largervolume of the gamut than is necessary. Virtual primaries that are closertogether may result in lower power consumption and decreased flicker inthe display—for example, two other operating characteristics for whichthe system could be optimized.

It may be desirable in some circumstances to increase the spread of thevirtual primaries beyond even the locations chosen by the bounding boxalgorithm. This may be accomplished by decreasing (or increasing) theangles after calculating them using the bounding box or survey method.

However the three planes are chosen, the three lines in CIE xy spacedescribe a triangle (or other suitable enclosed region) and theintersection points of the lines are three colors. These three colorscan be used as virtual primaries that can display any color that liesinside the triangle and thus inside the bounding box. These intersectionpoints can be found many different ways, one way is by converting thelines to CIE xy space and using line intersection formula. This mayrequire conversion to floating point so a method that leaves the planesin the linear RGB co-ordinate space may be desired. One such method thatmay not require floating point is to intersect each pair of the abovethree equations with a fourth plane that is perpendicular to the line ofgrays:

$\begin{matrix}{{\begin{pmatrix}r & g & b & 1 \\1 & 0 & 0 & 1 \\0 & 1 & 0 & 1 \\0 & 0 & 1 & 1\end{pmatrix}} = 0} & {{Equation}\mspace{14mu} 13}\end{matrix}$

The intersection of two of the rotated planes above may describe a lineradiating from the origin. Every point on the line may havesubstantially the same chromaticity. Any line that comes out of theorigin through the color cube should intersect the perpendicular planeof Equation 13 without integer overflow or divide by zero problems. Theresulting point should be one of the virtual primaries. It may beadvisable to scale all resulting virtual primaries until they touch theedge of the gamut. This allows that the LEDs may be bright enough toilluminate pixels between areas calculated with normal FSC colors andareas calculated with virtual primaries. Alternatively, it may bedesirable to scale the virtual primary colors down to the sameluminosity as the brightest color in the bounding box to reduce powerconsumption in the LED backlight and decrease the quantization errorimposed on the overlying LCD.

In another embodiment, the component colors of the virtual primaries maybe limited to the maximum duty cycle of each LED. For example, the redLED can be “on” fully in the first field of a frame and “off” in thefollowing two. Alternatively, the red LED can be on one third in allthree fields of a frame. In both these examples, the total power to thered LED is the same over time. This limit can be enforced by summing thered across all the virtual primaries and scaling it down until the totalmatches the duty cycle of the red LED. The same calculation may be donewith green, blue and any other LED primaries in the backlight. Theresult of these calculations are three colors—P₁, P₂ and P₃—thatdescribe a set of primary colors that in combination can produce any ofthe colors in the bounding box. This step may be accomplished by the“Calc virtual primaries” module 1832. These primaries may be laterloaded into the LED sequentially.

The point spread function of the LEDs may be used to interpolate thecolor of the virtual primaries in the LED backlight into an image withthe same resolution as the input sample points. This may be accomplishedby the “BackLight Interpolation” module 1834.

These results may be combined with the original RGB colors in “Calc. χValues” 1840 to produce values to be run through output gamma module1818 to convert them to the output quantization values available on thedisplay. The χ output values may be put in the LCD display 1824 whilethe virtual primaries are displayed sequentially in the LED backlight bythe FSC module 1820.

For displays systems that have the general form as the block diagram1800 that have point spread functions of the LEDs that overlap eachother, it is possible that there will be an overlap between steadybacklight LED point spread functions and dynamic virtual primary LEDpoint spread functions. In these cases, the resulting backlightillumination may be a mixture of steady and field sequential colorillumination. Each field may have a different color and brightness, butnot necessarily spread out enough to contain all of the colors using χvalues. This may mean that the χ values may not be able to reconstructall of the colors in this overlapping point spread function. In thesecases, it may be possible to find X/X_(L) and GMA values for each fieldthat are in gamut, especially for those pixels that are either darkerthan the average of the surrounding pixels or those that are nearer tothe LEDs that are steady and thus may exhibit lower spread caused bycontribution from the overlapping field sequentially modulated virtualprimary driving LEDs.

Using the X/X_(L) and GMA derived value for each field may have theadvantage of reducing the potential visibility of color break-up and/orflicker. Some colors may be in gamut, that is, they may be OOG for oneor more of the fields when using the X/X_(L) and GMA derived values andyet also be OOG for the value system. In such cases, the average valueof the illumination of the several virtual primary fields may be usefulin calculating and X/X_(L) and GMA derived value that will reconstructthe desired color. Stated another way, the sum of the overlapping steadystate and dynamic virtual primary fields over time may be used as if itwas a steady state illumination to calculate the X/X_(L) and GMA valuefor overlying pixels.

The above two methods of using the X/X_(L) and GMA values instead of χvalues may also be used in the areas that are illuminated by only thevirtual primaries controlled LEDs. This allows a display system to useonly virtual primaries, eliminating overlap between virtual primary andsteady, peak function 1804, derived LED point spread areas. In such asystem, it may be advantageous to attempt to reconstruct the desiredcolor in the following order, X/X_(L) and GMA derived values for eachvirtual primary field to reduce the potential for color break-up andflicker, followed by either the X/X_(L) and GMA derived values for theaverage color (sum) of the virtual primary fields or the χ derivedvalues for each virtual primary field.

Another method or mode of operation is to use “interim virtualprimaries”. Interim virtual primaries are a color set formed by theX/X_(L) and GMA that bound the desired color. This color set may then bepassed to the Calc χ Values block. The final values for the LCD may thenbe found by multiplying the X/X_(L) and χ values together. This methodor mode of operation may reduce the potential visibility of colorbreak-up and flicker.

Yet another method or mode of operation is to concentrate the brightnessof the steady backlight into one of four time slots to effectivelybecome a fourth field of a virtual primary field sequential colorsystem. With four virtual primaries, there may exist the possibility ofmetamers for desired colors and thus of metamer selection. One possiblemetamer may be to minimize the virtual primary this is furthest from thedesired color. If this minimum is zero, then the color may effectivelybe reconstructed by only three virtual primaries and may be calculatedusing the three virtual primary χ value calculation method describedabove.

It will be appreciated that this system is one of many possible systemsto handle OOG conditions. Other variations of this system are possibleand contemplated in the present application. For example, SPR could beimplemented/combined in this system as similar to the above.Additionally, many blocks (e.g. GMA, X/X_(L)) are repeated in FIG. 18;but other embodiments could reuse the same hardware to avoidduplication. Other methodologies of handling OOG conditions are possibleas well.

It will be similarly appreciated that other systems might employdifferent number of multiprimary backlights—e.g. R, G, B, C LEDs (whereC is cyan). The techniques of the above methods could be extendedsimilarly to calculate other chromaticity areas as is needed (e.g.quadrilaterals, triangles or other regions). In FIG. 23, the gamut ofallowable colors is expanded using a fourth color LED light emitter.This additional emitter may be substantially cyan colored as discussedearlier. Any set of virtual primaries 2330, 2340, 2350 may be created,for merely one example, with any allowable metameric combination of thecolor LED emitters. Since the color space that the virtual primaries maytake is larger than the traditional RGB primaries, one may use anysuitable primaries that will enclose the larger multiprimary colorgamut. In another embodiment, this set of primaries may be imaginary.That is to say, that they may be mathematically useful, but physicallyunrealizable. One such set of primaries is the CIE XYZ primaries. Sinceany realizable virtual primary may be described as a linear combinationof XYZ primaries, the RGB notation in the above calculations may bereplaced with XYZ notation with suitable transforms between the colorspaces, as is known in the art.

In an embodiment employing FSC techniques, it may be desirable to reduceFSC artifacts, such as color break-up and flicker. One approach may beto have the chromaticity areas not tightly bound to the distribution ofcolors found within each LED point spread function. Tight binding maygive rise to greater disparity in χ values—possibly causing a greaterchance of visible flickering.

Instead, it is possible to select virtual primaries that create avirtual gamut proportionally larger than the distributions of colorsfound in each LED point spread function. One method may be to move theprimaries by some fixed distance or proportional distance toward theoriginal RGB (or RGBC) primaries. Another method may be to find thecentroid of the virtual primaries, then move the virtual primaries awayfrom the centroid by some factor of the original distance. Anothermethod may be to find the average value of the colors found in the imagewithin the point spread function. The virtual primaries may be movedaway by some factor of the original distance, or they may be moved bysome function wherein they are proportionally moved further away whenthey are originally closer. A further refinement my be to weightbrighter colors more than dark colors, as bright colors that have largeinterfield χ value modulation will be more likely to cause visibleflicker.

As a solid color spanning an entire region of several LED point spreadfunctions has zero distribution, the virtual primaries collapse to thesame value. The desirability of using less primaries when possible maybe accomplished by setting two or even three of the primaries to thesame values. Additional logic may then combine the primaries and their χvalues should remain the same. This combining of primaries wherepossible increases the temporal frequencies, and thereby reducesartifacts. The smaller the spread of (or distribution of) the desiredpixel colors, the more likely this collapsing of virtual primaries.

Another embodiment may be to calculate the χ value error that is likelyto occur as the slow responding liquid crystal display from one state toanother to achieve the desired FSC modulation and adjust the virtualprimaries to compensate. In such a case, the bright primaries may bemade brighter and the dark primaries may be made darker.

Other FSC Techniques

It is possible for a FSC backlight system to employ Pulse WidthModulation (PWM) scheme to drive the backlights comprising, for example,LEDs. FIGS. 19A and 19B shows one embodiment of a single Pulse WidthModulation (PWM) cycle for a FSC system to handle OOG conditions. In theexample of FIG. 19A, suppose it is desired to exhibit a substantiallyred color which is slightly desaturated—so the green and blue LEDs areon slightly. Further in this example, suppose the red color to beexhibited is OOG (e.g. by about 2X in this example, as depicted as areaA1 in FIG. 19A). The red LED cannot come on bright enough to display it.FIG. 19B shows the virtual primary system at work—instead of displayingR G and B in the three time slots of the PWM cycle, it is displayingprimaries P1 (Red), P2 (red-orange) and P3 (dark magenta). It should benoted that the additional areas—A2 and A3—approximately equal the amountof OOG red area A1. So, the red curve in FIG. 19B now includes all theenergy of the red input value of FIG. 19A and the color is no longerOOG.

In yet another embodiment, FIG. 20A shows a FSC waveform that producessubstantially a white area in an LED backlight with the red, green andblue LEDs coming on sequentially to the roughly same amount. FIG. 20Bshows how the same white value can be produced by turning the LED's onat one third the brightness for three times as long in each cycle. Thisis as if the three virtual primaries P1, P2 and P3 were all set to thesame shade of grey. It is quite common for images to be black and white,grey scaled or to have large areas that have no color. It would beadvantageous to detect these areas and use monochrome virtual primarieslike FIG. 20B because this waveform would have no visible flicker whilethe waveform of FIG. 20A may have visible flicker. It may not bedesirable, however, to generate the waveforms of FIG. 20B. Instead thewaveform of FIG. 20C may be used, with the LEDs on proportional to thePWM scheme to produce the desired average brightness in a single FSCcycle. FIG. 20C may tend to have substantially reduced flicker becausethe flicker frequency is three times that of FIG. 20A and is beyond therange that the human visual system can detect it.

Dynamic Virtual Primary System Having Unfiltered LCD Display

Another embodiment of the present invention is shown in FIG. 21A, inwhich there are no color filters in the pixel pattern 2162 in theoverlying LCD 2160. This system operates with only “virtual primaryfield sequential color”, as described above. In operation, the R*G*B*perceptually encoded data is linearized by the “Input Gamma” module2105. An optional Input Filter 2110 may remove noise from the image. The“Bounding Box” module 2130 determines the color gamut map of the colorsto be displayed in the point spread function of each of the LEDs. Thisdata is used to calculate the virtual primaries in the “Calc VirtualPrimaries” module 2132. These virtual primaries are displayed on the LEDbacklight array 2120 by the “FSC” module 2125. The “BackLightInterpolation” module 2134 determines the actual color available behindeach pixel (i.e. unfiltered subpixel) of the LED 2160 by suitableinterpolation and the known point spread function of the LEDs. Thesevalues are combined with the RGB image data to calculate the χ values bythe “Calculate χ Values” module 2140. The χ values are gamma quantizedby the “Output Gamma” module 2115 to those levels available on the LCD2160.

With continued reference to FIGS. 21A and 21B, some example algorithmsare described for the each module. The following discussion assumes somesimplifying features of the backlight to simplify the description. Forexample, the LED backlight 2120 may be constructed to have triplets ofred, green and blue LEDs in a rectangular layout with each triplet closeenough together to be considered located at a single point. Each LED isassumed to have a rectangular point spread function. For the purpose ofmerely exposition of a single embodiment, it is assumed that theembodiment is constructed such that 8 LCD pixels are between each LEDand that there is an “extra” row of LED's at the edge of the LCD matrix.It will be appreciated that these assumptions will vary for othersystems constructed that fall within the scope of the presentapplication.

Noise in the input image, such as speckle, can cause the following stepsto decrease the dynamic range of the display or increase the powerconsumption in the LED backlight. For this reason it may be advantageousto add an optional Input Filter 2110 after Input Gamma module 2105 toremove this noise. Many image noise reduction filters are described inthe literature. One embodiment may be to filter the chromatic componentsin a suitable color space such as YCrCb or CIELAB. This will tend toreduce chromatic noise. Real images often contain information that isnot perceptible to the Human Vision System. Such information may causethe virtual primaries to be further apart than strictly needed if thatinformation is found in high spatio-chromatic frequencies. Suchchromatic noise is often found in the low light (dark) areas of animage. Filtering out such chromatic noise may allow a tighter, smallervirtual primary gamut with less variation in χ values, reducing thepotential for visible artifacts.

Because Equations 11 and 13 above have many zeros and ones in thematrices, the formula for the intersections of these planes can begreatly simplified. Calculating the actual angle between one of thecolor planes and an input color point may be computationally difficult,but there are other metrics that are easier to calculate and sort in thesame order as angles. The following three equations take an input color(r,g,b) and calculate one such metric:

rangle=2*r*MAXCOL/(2*r+g+b)

gangle=2*g*MAXCOL/(r+2*g+b)

bangle=2*b*MAXCOL/(r+g+2*b)

Where MAXCOL is the maximum integer value of an input color after inputgamma conversion in Module 2105. These formulas are simple enough thatthey may make surveying all the input points inside the point spreadfunction of an LED practical. In Bounding Box module 2130, all the inputpixels within the point spread function of an LED are converted topseudo-angles like this and the minimum (or the maximum) of thepseudo-angle to each axis may be found. With 8 LCD pixels between eachLED 2*8*2*8 or 256 input pixels may be surveyed to find the minimumangles for one backlight LED. Substantial savings in computation may bepossible by storing intermediate results in line buffers or framebuffers.

Once the minimum angles are found, these may be used in Calc VirtualPrimaries module 2132. As described above, the intersection of two ofthe planes in Equations 11 with the diagonal plane of Equation 13 mayresult in one of the virtual primaries. When the plane intersectionformula are expanded out into algebraic notation, a relatively simplecalculation results. Below is the calculation for the virtual primarythat is substantially close to the green axis:

Rp1=MAXCOL*rmin/(2*MAXCOL−rmin)

Gp1=MAXCOL*gmin/(2*MAXCOL−gmin)

Bp1=MAXCOL*(4*MAXCOL̂2−4*MAXCOL*gmin−4*rmin*MAXCOL+3*gmin*rmin)*(rmin*gmin−2*rmin*MAXCOL−2*MAXCOL*gmin+4*MAXCOL̂2)

Where rmin, gmin and bmin are the minimum values from surveying thesurrounding input color values with the pseudo-angle formula above. Theresult of this is the RGB co-ordinate of the virtual primary P1. Asimilar equation calculates the RGB co-ordinates of virtual primary P2:

Rp2=MAXCOL*(4*MAXCOL̂2−4*MAXCOL*bmin−4*MAXCOL*gmin+3*gmin*bmin)/(4*MAXCOL̂2−2*MAXCOL*bmin−2*MAXCOL*gmin+gmin*bmin)

Gp2=MAXCOL*gmin/(2*MAXCOL−gmin)

Bp2=MAXCOL*bmin/(2*MAXCOL−bmin)

And third, another set of similar equations calculates the RGBco-ordinates of virtual primary P3:

Rp3=MAXCOL*rmin/(2*MAXCOL−rmin)

Gp3=MAXCOL*(4*MAXCOL̂2−4*MAXCOL*bmin−4*MAXCOL*rmin+3*rmin*bmin)/(4*MAXCOL̂2−2*MAXCOL*bmin−2*MAXCOL*rmin+rmin*bmin)

Bp3=MAXCOL*bmin/(2*MAXCOL−bmin)

As described above, these virtual primaries may be scaled until theytouch the edge of the gamut for a maximum brightness display.Alternatively, they can be scaled to the maximum brightness of the inputcolors inside the point spread function of the LED. If Bounding Boxdown-sample module 2130 calculated the maximum brightness whilesurveying the minimum angles and stored it in variable Lmax, theequations for doing the scaling might take the form:

Rp1=Rp1*Lmax/max(Rp1,Gp1,Bp1)

Gp1=Gp1*Lmax/max(Rp1,Gp1,Bp1)

Bp1=Bp1*Lmax/max(Rp1,Gp1,Bp1)

Rp2=Rp2*Lmax/max(Rp2,Gp2,Bp2)

Gp2=Gp2*Lmax/max(Rp2,Gp2,Bp2)

Bp2=Bp2*Lmax/max(Rp2,Gp2,Bp2)

Rp3=Rp3*Lmax/max(Rp3,Gp3,Bp3)

Gp3=Gp3*Lmax/max(Rp3,Gp3,Bp3)

Bp3=Bp3*Lmax/max(Rp3,Gp3,Bp3)

Also as described above, it may be desirable to limit the total power ofeach LED. In this example with three virtual primaries, limiting the sumof the red in all three to the maximum color value allowed may result ina duty cycle of ⅓. The same is true for green and blue LEDs. Thiscalculation may not be needed if the sum of the red values in all threevirtual primaries is already less than MAXCO. Thus the pseudo-code maytake the following form:

Div = math.max(Rp1+Rp2+Rp3,Gp1+Gp2+Gp3,Bp1+Bp2+Bp3) if Div > MAXCOL thenRp1 = Rp1*MAXCOL/Div Gp1 = Gp1*MAXCOL/Div Bp1 = Bp1*MAXCOL/Div Rp2 =Rp2*MAXCOL/Div Gp2 = Gp2*MAXCOL/Div Bp2 = Bp2*MAXCOL/Div Rp3 =Rp3*MAXCOL/Div Gp3 = Gp3*MAXCOL/Div Bp3 = Bp3*MAXCOL/Div end

When an area of the display is substantially monochrome, the virtualprimaries may lie close together on a chromaticity diagram and may havesubstantially identical values. The calculations above may result in thethree virtual primaries having values near ⅓ their maximum in eachfield, but adding up to 100% in a whole frame. However, when an area ofthe image has high chromatic spatial frequencies, the virtual primariesmay be very far apart. In that case, the equations above may allow eachvirtual primary to have most of its power in one field, since in thiscase it will be off or low power in the other fields of the same frame.

The power reduction calculations above may work well when the pixelsinside the point spread function of an LED are substantially monochrome,but may not find the lowest power in areas with high chromatic spatialfrequencies. Another embodiment to decrease the power in the LEDbackbuffer might be to survey the largest χ values inside the pointspread function of each LED. This maximum χ value can then be used toscale the LEDs down to the lowest possible values. However, the χ valuesmay not be calculated until later in Calc χ Values module 2140. Oneembodiment may be to have a duplicate Backlight Module 2134 andduplicate Calculate χ Values module 2140 inside Calc Virtual Primariesmodule 2132. This is shown in FIG. 21B. First LED Approximation module2135 would perform the calculations described above for Calc VirtualPrimaries Module 2132. The duplicate modules 2134 and 2140 wouldcalculate a first approximation of the χ values. Then these χ values maybe analyzed by Survey Max χ Values to find the largest value in thepoint spread function of each LED. Then the final value of each LED maybe calculated by Scale LED Values module 2152. These last two stepscould be implemented using the following pseudo-code:

for j=0,15 do survey the max xhi value in the point spread function(PSF) for i=0,15 do loop for all pixels in PSF localxhi=spr.fetch(“LCD”,x*8+i−8,y*8+j−8,xbuf) fetch the xhi valuemaxhi=math.max(maxhi,xhi) find the maximum one end pixels in PSF endlines in PSF local r,g,b=spr.fetch(ledbuf,x,y) read in LED buffer valuesmaxhi=math.max(MAXCOL,maxhi+floor) prevent zero valued determinants Dr=r*maxhi/MAXCOL Scale LED Values g=g*maxhi/MAXCOL b=b*maxhi/MAXCOLspr.store(ledbuf,x,y,r,g,b) store them back in LED buffer

This algorithm may be repeated for each LED triplet in each of the threefields. This second approximation of the LED values may havesubstantially reduced values and reduced power consumption.

The embodiment above produces the calculation of the virtual primariesfor a single LED in all three fields of a frame. In FIG. 21A these LEDvalues above are passed to FSC module 2125, which may include a smallLED frame buffer for storing them.

Backlight Interpolation module 2134 may use the values from the LEDframe buffer to calculate the effective backlight color under each pixel2162 in LCD matrix 2160. It may be possible to do this calculation onthe fly as pixels are displayed, or it may be desirable to pre-calculateall the effective backlight colors and store them in another framebuffer. If so, three frame buffers may be used to store the effectivebacklight colors for all three fields of a single frame. Each locationin each of these buffers may be calculated from at most 4 surroundingLEDs in this example configuration. The equations below may use apoint-spread function stored in a look-up table named spread. In thisexample, the values in this table are eight 12 bit integers with 4096being the encoding for the brightness directly over the LED. Thefollowing equations calculates one effective backlight color (rs,gs,bs)for one location (x,y) in one field:

xb=x/8

yb=y/8—position of a nearby LED

xd=mod(x,7)

yd=mod(y,7)—distance to a nearby LED center

Rp,Gp,Bp=fetch(xb,yb)—get upper left LED color

psf=spread[xd]*spread[yd]/4096—look up point spread function

rs=Rp*psf—sum upper left LED

gs=Gp*psf

bs=b*psf

Rp,Gp,Bp=fetch(xb+1,yb)—color of upper right LED

psf=spread[7−xd]*spread[yd]/4096—PSF for this led and pixel

rs=rs+Rp*psf—sum upper left LED

gs=gs+Gp*psf

bs=bs+Bp*psf

Rp,Gp,Bp=spr.fetch(ledbuf,xb,yb+1)—color of lower left LED

psf=spread[xd]*spread[7−yd]/4096—PSF for this led and pixel

rs=rs+Rp*psf—sum upper left LED

gs=gs+Gp*psf

bs=bs+Bp*psf

Rp,Gp,Bp=fetch(xb+1,yb+1)—color of lower right LED

psf=spread[7−xd]*spread[7−yd]/4096—PSF for this led and pixel

rs=rs+Rp*psf—sum upper left LED

gs=gs+Gp*psf

bs=bs+Bp*psf

rs=rs/4096—sum was 12-bit precision

gs=gs/4096—collapse them back to pixel precision

bs=bs/4096

A calculation like the pseudo-code above may be performed for each pixelin each field of the frame. The resulting values may be used by the Calcχ Values module 2140. This module may use the expanded Equation 10 fromabove to calculate the χ values for each LCD pixel in all three fields.This equation involves a matrix inversion, however, and not every matrixcan be inverted. So first the determinant of the matrix may becalculated and tested to make sure it is not zero. If it is not, thenEquation 10 can be used almost exactly as is. In actual use, the pixelvalues are integers between 0 and the maximum possible value MAXCOL, soan additional factor of MAXCOL is required in each calculation. In thefollowing pseudo-code, the values (R1,G1,B1) is the effective backlightcolor from the first field at a single location, (R2,G2,B2) and(R3,G2,B3) are the effective backlight colors from the second and thirdfield of a frame. And (R,G,B) is the input color at that location in thedisplay after Input Gamma module 2105.

D = R1*G2*B3−R1*B2*G3−R2*G1*B3+R2*B1*G3+R3*G1*B2−R3*B1*G2 if D!=0 thenx1 = ((G2*B3−B2*G3)*R+(R3*B2−R2*B3)*G+ (G3*R2−R3*G2)*B)*MAXCOL/D x2 =((B1*G3−G1*B3)*R+(R1*B3−B1*R3)*G+ (R3*G1−R1*G3)*B)*MAXCOL/D x3 =((G1*B2−B1*G2)*R+(B1*R2−R1*B2)*G+ (R1*G2−G1*R2)*B)*MAXCOL/D end

These calculations may allow a region of the display that issubstantially monochrome to display the same value in all three fieldsof a frame, reducing flicker. This may work with black and white imagesor areas of an image that are monochromatic in any color. For oneexamples of this, consider a ramp of red, or a picture taken under redlight in a darkroom. Images that have some colored areas and othersmonochrome may tend to switch to this low-flicker mode inside monochromeareas that are sufficiently far away from colored areas (beyond thepoint spread function of the LEDs). The calculations above may be donefor each input pixel value and passed on to Output Gamma module 2115 andthen to LED matrix 2160, the χ1, χ2 and χ3 values each in their ownfield of the frame.

The system in FIG. 21A allows the backlight array 2120 to beindividually controlled. In some embodiments, the LEDs, or other coloredlight sources, may not be individually spatially controlled, only itsoverall intensity. In such a case, the point spread function becomes aglobally uniform function. The BackLight Interpolation function 2134becomes redundant. Such a system still shows reduced field sequentialcolor artifacts since most images to be displayed are likely to have agamut map smaller than the full gamut range of the color primaries ofthe backlight array 2120. This embodiment may be useful in colorprojectors in which colored light from controllable sources such as LEDsor laser pumped frequency converters (non-linear optical devices) areintensity modulated in sequential fields.

In the discussion within this present application, a dynamic fieldsequential display device is described that may suffice if it comprisesa backlight, wherein the backlight is capable of illuminating aplurality of colors and a plurality of intensities of said colors,wherein said colors and intensities of said colors may be independentlyreproducible across a set of regions forming the backlight; and if itfurther comprises control circuitry for dynamically selecting the colorand intensity of the backlight at a given region. This selection may befurther dependent upon the input color values at a given region. As maybe appreciated, conventional field sequential display devices tend notto have independent controls over both the intensity and color of aregion of the image at any given point in time and further such controlsare not dependent upon the input color values at a point in time and tooptimize for certain operating criteria.

Segmented Backlight

Having now discussed various embodiments for display systems havingnovel backlighting arrangements and methods for operating the same, itwill now be described display systems having novel backlights, e.g.segmented, that extend the above described system and methods ofoperation. These novel backlights may also tend to lower the cost of thebacklight for such novel displays as such systems may employ a reducednumber of light elements to achieve substantially similar improvementsin dynamic contrast and other benefits associated with the array versionof such display systems.

In one embodiment, a display system comprises a backlight outputtinglight in accordance with a first control signal, said backlightcomprising: a plurality of N+M light guides, wherein N light guidesdisposed in a first direction and M light guides disposed a seconddirection, said light guides overlapping and forming a N×M set ofoptically communicating intersections; a plurality of N+M individuallyaddressable light emitter units, each of said N+M light emitter unitbeing associated with and optically connected to one of said N+M lightguide respectively; each light emitter unit capable of producing broadspectrum light for in one of a plurality of colors; a spatial lightmodulator for displaying an output color image, said spatial lightmodulator receiving light from said backlight and modulating said lightin accordance to a second control signal; and controller circuitry forproviding said first signal and said second signal, said controllercircuitry receiving input color image data and determining said firstand said second control signals and outputting said first signal to saidplurality of individually addressable light emitter units and outputtingsaid second control signal to said spatial light modulator such that thecombination of said light from said backlight and modulated by saidspatial light modulator produces an output image based upon said inputcolor image data.

Display System Comprising Multiple Segmented Backlight

As discussed above, the backlight of many embodiments may comprise anarray of emitters (e.g. backlight 120 of FIG. 1A) operated as a lowresolution imaging device that is convolved with a higher resolution LCDoverlying it. To achieve a given N×M backlight resolution, N×M number ofemitters 122 (or cluster of emitters for color or added brightness) isneeded in array-type configurations. In contrast, referring to FIG. 25which shows one embodiment of the present invention, novel backlight2500 may achieve approximately N×M resolution by using approximately N+Mnumber of emitters 2512 & 2522. The manner in which this may be achievedand the methods by which this novel backlight 2500 may be operated willbe explained below.

Consider the prior art backlight 2600 shown in FIG. 26. It is comprisedof a flat light guide 2610 and two light emitters 2612. The flat lightguide 2610 includes features on at least one surface features tofrustrate the total internal reflection, redirecting light toward anoverlying spatial light modulator. The light emitters 2612 may be coldcathode fluorescent lamps (CCFL) as is commonly used in the art or othersuitable light emitters such as Light Emitting Diodes (LED).

As taught in U.S. Pat. No. 5,717,422 to Fergason entitled “VariableIntensity High Contrast Passive Display” (and included herein byreference), the brightness of the light emitters 2612 may be controlledso as to dim the backlight 2600 in response to an image with less thanfull brightness while the overlying spatial light modulator, such as anLCD, is adjusted to allow more light to pass. The convolution of thereduced backlight 2600 brightness and increased transmittance of thespatial light modulator may maintain the desired image brightness whilereducing light emitter 2612 power requirements and concomitantlyincreasing contrast of the spatial light modulator. However, if even asingle pixel in the input image is at full brightness, the backlightemitter 2612 brightness must be also at full brightness if the image isto be reproduced with full fidelity.

One embodiment of an improved backlight is depicted in FIG. 27. As maybe noted, backlight 2700 is divided in two (or possibly more) opticallyseparate light guides 2720 and 2721 that are coupled to light emitters2722 and 2723 respectively. This may allow the light emitters 2722 and2723 to have different brightness levels at a same time. Thus, if onepixel in half of the image is at full brightness, but the other half ofthe image is at a lower brightness, at least that half of the image mayallow for a lower light emitter brightness. Statistically, thisarrangement may allow for lower overall average light emitter brightnessand power drain with potential concomitant image improvement.

The process of segmenting the backlight may proceed further to increasethe statistical improvement. FIG. 28 show a prior art backlight 2800arrangement which is comprised of a flat light guide 2810 and four lightemitters 2812. As before the light emitters 2812 may be CCFLs or LEDs.Novel backlight 2900 shown in FIG. 29 comprises four optically separatelight guides 2910, 2914, 2920 & 2924. Light emitters 2912, 2916, 2922, &2926 may then be exclusively coupled to light guides 2910, 2914, 2920 &2924 respectively. For example, one pair of light guides 2920 & 2924 aredivided along the horizontal axis, allowing for separation of the lowerand upper half brightness level by independently controlled andexclusively coupled light emitters 2922 & 2926. Another pair of lightguides 2910 & 2914 may lay either beneath or on top or pair 2922 & 2926.This pair of light guides 2910 & 2914 is divided along the verticalaxis, allowing for separation of the right and left half brightnesslevel by independently controlled exclusively coupled light emitters2912 & 2916. This may allow all four of the light emitters 2912, 2916,2922, & 2926 to have different brightness levels.

In operation, if one pixel in a quarter (e.g. in 2930) of the image wereat full brightness, but the other three quarters of the image were at alower brightness, at least that portion of the image may allow for alower light emitter brightness. For example, suppose an image has anumber of pixels on at full brightness in just one corner of the image,and the rest of the image is at a very low brightness. Assume that thefull bright portion of the image occurs in the upper right corner. Theupper light emitter 2922 and the right hand emitter 2912 would be turnedon to full brightness while the lower light emitter 2926 and left handemitter 2916 would be set at the very low brightness. The upper righthand quadrant 2930 would be illuminated at full brightness. The upperleft hand 2932 and lower right hand 2934 quadrants would be illuminatedat an intermediate brightness. The lower left hand quadrant 2936 wouldbe illuminated at a very low brightness. Statistically, this arrangementmay allow for lower overall average light emitter 2912, 2916, 2922, &2926 brightness and power drain than the backlight 2800 in FIG. 28 withpotential concomitant image improvement over the backlight 2700 in FIG.27.

Likewise, the process of segmenting may proceed further to increase thestatistical improvement of power and image quality. Shown in FIG. 30, abacklight 3000 may be formed from a matrix of overlapping light guides.In this example of the present invention, each quadrant is anindependent matrix of light guides. Some number of the light guides 3020with exclusively coupled light emitters 3022 could be primarily disposedin columns while some other number of the light guides 3010 withexclusively coupled light emitters 3012 could be primarily disposed inrows.

In this embodiment, to achieve approximately a N×M low resolutionbacklight, it is seen in FIG. 30 that this may be achieved by use of2×(N+M) light guides and emitters—with two columns (e.g. at the rightand left side of the backlight 3000) and two rows (e.g. at the top andbottom of backlight 3000) of emitters. In yet another embodiment, asimilar N×M low resolution backlight is possible with the use of N+Mlight guides and emitters. This is achieved by use of only one column(e.g. at either the right or left side of the backlight) and one row ofemitters (e.g. either the top or bottom of the backlight) and one lightguide per row and column. Such an embodiment has the same number ofmatrix cross connections at the row and column intersections and may bea lower cost option. However, it may lose a bit of the statisticaladvantages of the backlight of FIG. 30 and the commensurate gain inpower consumption. Additionally, as previously noted, emitters 3022 maybe either white emitters or a combination of one or more coloredemitters. Other embodiments making use of these principles are of coursepossible and are contemplated within the scope of the presentapplication.

FIG. 31 shows a cross section of a backlight 3100 with one light guide3110 primarily disposed in a row lying underneath a plurality of lightguides 3120 disposed in columns. In the cross section of the backlight3100, light ray beam 3130 is trapped in the light guide 3110 by totalinternal reflection until portions of the light rays 3135 are scattered,deflected into high angles that may escape by features 3140 on onesurface of the light guide. These escaping light rays 3135 may passthrough the overlying column light guides 3120. Likewise, light may alsobe trapped and subsequently scattered by the overlying light guides3120. In operation, where both light guides are illuminated at fullbrightness, the scattered light from both light guides 3110 & 3120 willsum to full brightness. Where both are not illuminated, no light may beseen at their intersections. Where one light guide is illuminated andanother is not, the light will sum to a lower value equal to thecontribution from the illuminated light guide. Thus, a backlight made inaccordance with the principles disclosed herein (e.g. backlight 200) maybe considered, by analogy, as an N×M display with very high crosstalk inthe rows and columns.

Such a segmented backlight with very high crosstalk may be advantageousfor variety of display systems. For example, FIGS. 32A and 32B are twoblock diagrams of display systems might employ such a backlight, onewith a monochrome front panel and one with a colored subpixelated frontpanel respectively. FIG. 32A depicts the block diagram of display system3200 using a segmented backlight 3220 to illuminate a transmissivespatial light modulator 3260, such as a monochrome LCD. Typically, thespatial light modulator 3260 would be higher resolution than backlight3220, but may be the same or even lower.

In operation, system 3200 could accept an input image data stream, suchas e.g. a perceptually, gamma, digitally quantized R*G*B* image. Suchdata may be linearized by Gamma Function 3205. This linear RGB signalmay be surveyed by Peak Function 3210 to find the peak brightness valuesof for pixels that map to, or lie within the area illuminated by, therows and columns of the matrix backlight 3220. In one embodiment, lightemitters 3222 could be broad spectrum, for instance, white lightsources. In such a case, the RGB values may be surveyed for the maximumred, green, or blue values that map to each given column and each givenrow.

In another embodiment, light emitters 3222 could be comprised ofindependently controllable color primaries such as red, green, and blue.In such a case, the RGB values may be surveyed for the maximum red,green, and blue values that map to each given column and each given rowindependently. When the image to be rendered during a given frame isanalyzed prior to assigning intensity values to individual coloredemitters, there are certain degrees of freedom and constraints that maybe taken into account. For merely one example, if in row M the maximumvalue for red across row M required by the image is a middle rangeintensity value and such maximum value is localized to, for example, oneparticular intersection of orthogonal light guides (say at (M, S) whereS is the column number of that intersection), then that red intensitymay be split between the red emitter for row M and the red emitter forcolumn S.

One possible assignment of intensity values would be to set the redemitters of both column S and row M sufficiently such that each wouldseparately contribute the required red intensity value at intersection(M,S)—and allow the front panel to restrict the amount of red light tothe proper required level. However, such a choice might not be optimalfrom a power savings perspective. Another embodiment might be to assignall the red light from one red emitter (either row or column, ifpossible) and to reduce the amount in the other emitter. In such anembodiment, the uses of second order statistics might provide animprovement. For example, if it were the case that the middle rangeintensity value for red at (M, S) were also the local maximum acrosscolumn S, then choice of red intensity for the two red emitters may beinfluenced by the next highest red intensity value required for column Mand row S. The choice of intensity values for colored emitters wouldselected according to many possible optimization schemes—with thealgorithm optimizing for many possible metrics, e.g. power savings, etc.

In addition to spatial considerations for assigning intensity values,temporal consideration may also be used—either alone or in combinationwith spatial considerations. For example, another mode of operation maybe to scan rows or columns with the desired illumination. For example,the columns may be kept dark save for one column at a time, beingilluminated for a brief time. This may proceed in an ordered or randomfashion. It may be in an orderly sequence from top to bottom or bottomto top. Similarly, the rows may be scanned in an ordered or randomfashion. It may be in an orderly sequence from right to left or left toright. This scanning sequence may be in phase or step with the addressscanning of the spatial light modulator illuminated by the backlightsuch that it allows the modulator, such as LCD pixels, to reach desiredtransmittance values before being illuminated.

With continued reference to FIG. 32, Peak Function 3210 output may be aform of matrix encoded down sampled image, denoted by the down arrow.The peak values may then be sent to Backlight Controller 3212 andsubsequently to the light emitters 3222 of the backlight 3220. The peakvalues may also be sent to Backlight Interpolation block 3205 which maycalculate the illumination that is present under each pixel of the imageto be rendered on the spatial light modulator 3260. Such calculationsmay be accomplished according to a theoretical model of illuminationbased upon image data values. Alternatively, the calculations may bebased on empirical data of measured illumination according to image datavalues applied.

Backlight Interpolation 3205 output may be an upsampled image denoted bythe up arrow representing the backlight 3220 illumination X_(L). Thelinear RGB image values X may then be divided by the interpolatedbacklight illumination values X_(L) in the X/X_(L) block 3236. TheX/X_(L) image may then be gamma correction quantized to match the gammaof the display in the Gamma Correction (γ⁻¹) block 3215. When thebacklight 3220 illumination X_(L) is convolved with the X/X_(L) image onthe spatial light modulator 3260, the desired image X may then bereconstructed.

The matrix backlight may also improve subpixel rendered RGBW or othermultiprimary display systems. FIG. 32B depicts a block diagram of adisplay system 3201 using segmented backlight 3220 to illuminate atransmissive multiprimary (e.g. RGBW, RGBC, RGBY and the like) colorfiltered 3265 spatial light modulator 3260 such as an LCD using one ofthe layouts taught in several of the co-owned patent applicationsmentioned above. An incoming perceptually, gamma, digitally quantizedR*G*B* image is linearized by the Gamma Function 3205. The linear RGBsignal is surveyed by the Peak Function 3210 to find the peak brightnessvalues of pixel that map to, lie within the area illuminated by, therows and columns of the matrix backlight 3220. For light emitters 3222that are broad spectrum, for instance, white light sources, the RGBvalues may be surveyed for the maximum red, green, or blue values thatmap to each given column and each given row in a manner taught in (newbacklight control app). For light emitters 3222 which are comprised ofindependently controllable color primaries such as red, green, and blue,the RGB values may be surveyed for the maximum red, green, and bluevalues that map to each given column and each given row independently.The Peak Function's 3210 output could be in a form of matrix encodeddown sampled image, denoted by the down arrow. The peak values may thenbe sent to the Backlight Controller 3212 and subsequently to the lightemitters 3222 of the backlight 3220. The peak values may also be sent tothe Backlight Interpolation block 3205 which calculates the illuminationthat is present at each pixel of the image to be rendered on the spatiallight modulator 3260

The Backlight Interpolation's 3205 output may be an upsampled imagedenoted by the up arrow representing the backlight 3220 illuminationX_(L). The linear RGB image values X may be divided by the interpolatedbacklight illumination values X_(L) in the X/X_(L) block 3236. The RGBX/X_(L) image may then be converted to an RGBW X/X_(L) image in theGamut mapping Algorithm (GMA) block 3240 using any suitable GMA method.This RGBW X/X_(L) image may then be subpixel rendered, possibly usingany suitable method described herein. The subpixel rendered RGBW X/X_(L)image may then be gamma correction quantized to match the gamma of thedisplay in the Gamma Correction (γ⁻¹) block 3215. When the backlight3220 illumination X_(L) is convolved with the subpixel rendered RGBWX/X_(L) image on the spatial light modulator 3260, the desired image Xmay be reconstructed.

The matrix backlight may also improve Field Sequential Color systems.Consider the block diagram 3300 of a display system using a segmentedbacklight 3320 to illuminate a transmissive spatial light modulator3360. An incoming perceptually, gamma, digitally quantized R*G*B* imagemay be linearized by the Gamma Function 3305. The linear RGB signal maybe surveyed by the Bounding Box block 3330 to find the smallest box thatbounds the color and brightness values of pixels that map to, lie withinthe area illuminated by, the rows and columns of the matrix backlight3320. The values from the Bounding Box block 3330 may be used tocalculate a set of virtual primaries in the Calc Virtual Primaries block3332. These virtual primary values may then be used by the FSC tocontrol the field sequential color brightness values of the lightemitters 3322 in the segmented backlight 3320. It may be noted thatthese emitters may be comprised of red, green, blue LEDs, or red, green,blue, and cyan (or emerald green) LEDs in this or in any hereinmentioned embodiment. The color and brightness of the light emitters3320 may also be sent to the Backlight Interpolation block 3334 whichcalculates the illumination that is present under each pixel of theimage to be rendered on the spatial light modulator 3360.

The Backlight Interpolation's 3334 output may be an upsampled imagedenoted by the up arrow. Using the interpolated illumination and linearRGB values to be rendered, the χ values are found by the Calc χ Valuesblock 3340. These χ values are the relative transmission values thatwhen convolved with the backlight illumination values for each of thecolor fields may sum substantially to the desired color to be renderedon the display. The χ values may be gamma corrected and quantized tomatch the transmissive spatial light modulator's 3360 quantizedelectro-optical transfer function by the Output Gamma block 3315.

It may be instructive to consider the case of a black&white movie on TVwith a color station icon in the corner. Most of the columns and rows ofthe matrix light backlight 3320 will have virtual primaries thatcollapse to varying levels of grey. The column(s) and row(s) thatintersect at the icon may have virtual primaries that have a large colorgamut. At the intersection, this gamut may be substantially fullyavailable. Those portions of each of the column(s) and row(s) thatintersect with the columns and rows illuminated by levels of grey mayblend in a substantially linearly manner with the wide color gamutvirtual primaries to form pastel virtual primaries with a reduced colorgamut spread. The Backlight Interpolation block 3334 will note this andthe Calc χ Values block 3340 will compensate accordingly. The finalresult may be a black&white image with a substantially full color iconin the corner, possibly with very little, if any, color break-up visiblein the rendered image.

While the techniques and implementations have been described withreference to exemplary embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe appended claims. In addition, many modifications may be made toadapt a particular situation or material to the teachings withoutdeparting from the essential scope thereof. Therefore, the particularembodiments, implementations and techniques disclosed herein, some ofwhich indicate the best mode contemplated for carrying out theseembodiments, implementations and techniques, are not intended to limitthe scope of the appended claims.

1. A display system comprising: a spatial light modulator for displaying an output color image formed from input image color data; the spatial light modulator substantially comprising a subpixel repeating group including subpixels in a plurality of primary colors; a plurality of individually addressable colored light emitters disposed as a backlight to provide light for forming the output color image on the spatial light modulator; each light emitter producing light in one of a plurality of colors; and controller circuitry for controlling light from the plurality of individually addressable colored light emitters; the controller circuitry using the input image color data to determine a value for each of the individually addressable colored light emitters such that an output image color in one of the subpixels of the spatial light modulator depends on the color of the light from the light emitters.
 2. The display system of claim 1 wherein the plurality of individually addressable colored light emitters produce light in the plurality of primary colors of the subpixel repeating group.
 3. The display system of claim 1 wherein the plurality of individually addressable colored light emitters produce light in the saturated primary colors of the subpixel repeating group.
 4. The display system of claim 1 wherein the plurality of individually addressable colored light emitters producing light in at least one of the saturated primary colors of the subpixel repeating group is tuned to produce light having a specific range of wavelengths for the saturated primary color.
 5. The display system of claim 1 wherein the plurality of individually addressable colored light emitters produce light in red, green, blue and cyan colors.
 6. The display system of claim 1 wherein the subpixel repeating group includes a clear subpixel as one of the plurality of primary colors; and wherein the controller circuitry controls the color of the light from the light emitters such that the clear subpixel functions as a backlight controlled primary color to produce the output color image.
 7. The display system of claim 6 wherein the controller circuitry controls the color of the light from the light emitters such that the clear subpixel functions as a first backlight controlled primary color in a first region of the output color image and functions as a second backlight controlled primary color in a second region of the output color image.
 8. The display system of claim 1 wherein the controller circuitry performs a peak function operation using the input image color data to produce, for each light emitter in a first color, a peak value of the first color in a region of the input image color data corresponding to a local area of a point spread function support of the light emitter.
 9. The display system of claim 1 wherein the controller circuitry further uses the values for each of the individually addressable colored light emitters to produce a low resolution version of the input image color data.
 10. The display system of claim 1 wherein the spatial light modulator is a liquid crystal display panel.
 11. The display system of claim 1 wherein the plurality of individually addressable colored light emitters comprises an array of light emitting diodes.
 12. The display system of claim 1 wherein the input image color data is specified as one of red, green and blue color values, red, green, blue, and cyan color values, red, green, blue, and emerald color values, and YCbCr color values.
 13. A display system comprising: a multi-primary spatial light modulator for displaying an output color image formed from an input signal comprising a frame of color input values; the frame having a first image resolution; the spatial light modulator substantially comprising a subpixel repeating group including subpixels in at least four primary colors; a plurality of individually addressable colored light emitters disposed as a backlight to provide light for forming the output color image on the spatial light modulator; each light emitter producing light in one of at least four primary colors; a first gamut mapping operation for converting each color input value to a first multi-primary color signal in the color space of the plurality of individually addressable colored light emitters; the first gamut mapping operation producing a frame of converted color values; controller circuitry for filtering the frame of converted color values to produce a frame of filtered color values having a second, lower resolution than the frame of color input values; the individually addressable colored light emitters displaying the frame of filtered color values; an interpolation operation for calculating brightness values and color values from the frame of filtered color values at each location of the frame of input color values; a second gamut mapping operation for converting each color input value to a second multi-primary color signal in the color space of the spatial light modulator using the brightness values and color values calculated by the interpolation means; and a subpixel rendering operation for filtering the second multi-primary color signal for display on the spatial light modulator at the same time as the individually addressable colored light emitters display the frame of filtered color values.
 14. The display system of claim 13 wherein the color input values are specified according to a set of input primary colors, and wherein first gamut mapping operation converts each color input value from the color space of the input primary colors to the first multi-primary color signal in the color space of the plurality of individually addressable colored light emitters.
 15. The display system of claim 13 wherein the controller circuitry filters the frame of converted color values using a maximum brightness function that computes a maximum brightness in an area of the frame of input color values overlying a first one of the plurality of individually addressable colored light emitters.
 16. The display system of claim 13 wherein the controller circuitry filters the frame of converted color values using one of a sync function and a windowed sync function.
 17. The display system of claim 13 wherein the first gamut mapping operation includes a metamer select function for selecting a metamer for the first multi-primary color signal.
 18. The display system of claim 13 wherein the interpolation operation uses a point spread function of one of the plurality of individually addressable colored light emitters for calculating brightness values and color values from the frame of filtered color values at each location of the frame of input color values.
 19. The display system of claim 13 wherein the subpixel repeating group of the spatial light modulator includes a white (clear) subpixel as one of the at least four primary colors, and includes at least three saturated primary colors; and wherein the subpixel rendering operation uses the white subpixel as an additional reconstruction point for one of the saturated primary colors.
 20. A display system comprising: a spatial light modulator for displaying an output color image formed from an input signal comprising a set of color input values; the spatial light modulator substantially comprising a set of individually controllable transmissive elements; a plurality of individually addressable colored light emitters disposed as a backlight to provide light for forming a color image on the spatial light modulator; each light emitter producing light in one of a plurality of primary colors; for a plurality of regions, said regions comprising a set of point spread functions of a set of said light emitter, a first mapping operation for selecting a set of virtual primaries that bound each color input value within each said region, said virtual primaries comprising a plurality of intensities of said plurality of said light emitters within said set of point spread functions; field sequential control circuitry for controlling the duration and illumination of said virtual primaries over a set of fields comprising an intermediate color signal formed by said light emitters within each said region to produce an intermediate color image onto said spatial light modulator; and circuitry for controlling said set of transmissive elements within each said region to modulate said intermediate color image to produce said output color image.
 21. The display system of claim 20 wherein one of said plurality of regions further comprises one transmissive element upon said spatial light modulator within a set of point spread functions of a set of light emitters.
 22. The display system of claim 20 wherein one of said plurality of regions is the entire set of transmissive elements upon said spatial light modulator.
 23. The display system of claim 20 wherein said set of virtual primaries is selected to optimize the performance of said display system according to a set of operating criteria.
 24. The display system of claim 23 wherein said set of operating criteria comprises at least one of a group, said group comprising: reducing flicker, reducing power consumption, reducing color breakup, increasing dynamic range, and reducing quantization error.
 25. The display system of claim 23 wherein said set of virtual primaries is selected to minimize the difference of luminance of said virtual primaries.
 26. The display system of claim 23 wherein said field sequential control circuitry controls the duration and illumination of said virtual primaries to optimize the performance of said display system according to a set of operating criteria.
 27. The display system of claim 26 wherein said set of operating criteria comprises at least one of a group, said group comprising reducing out of gamut conditions and reducing power consumption.
 28. The display system of claim 20 wherein said circuitry for controlling said set of transmissive elements further comprises selecting a set of coefficient values for each transmissive element to control the modulation of said intermediate color image for each field in which a virtual primary is illuminated.
 29. A dynamic field sequential display device comprising: a backlight, said backlight capable of illuminating a plurality of colors and a plurality of intensities of said colors, said colors and intensities of said colors being independently reproducible across a set of regions forming the backlight; control circuitry for dynamically selecting the color and intensity of the backlight at a given region, said selection dependent upon input color values within said region.
 30. The dynamic field sequential display device of claim 29 wherein said plurality of colors further comprising a set of virtual primaries, said virtual primaries selected depending upon said input color values and to optimize the performance of the display system according to a set of operating criteria.
 31. The display system of claim 30 wherein said set of operating criteria comprises at least one of a group, said group comprising: reducing flicker, reducing power consumption, reducing color breakup, increasing dynamic range, reducing quantization error and reducing out of gamut conditions.
 32. A display system comprising: a backlight outputting light in accordance with a first control signal, said backlight comprising: a plurality of N+M light guides, wherein N light guides disposed in a first direction and M light guides disposed a second direction, said light guides overlapping and forming a N×M set of optically communicating intersections; a plurality of N+M individually addressable light emitter units, each of said N+M light emitter unit being associated with and optically connected to one of said N+M light guide respectively; each light emitter unit capable of producing broad spectrum light for in one of a plurality of colors; a spatial light modulator for displaying an output color image, said spatial light modulator receiving light from said backlight and modulating said light in accordance to a second control signal; and controller circuitry for providing said first signal and said second signal, said controller circuitry receiving input color image data and determining said first and said second control signals and outputting said first signal to said plurality of individually addressable light emitter units and outputting said second control signal to said spatial light modulator such that the combination of said light from said backlight and modulated by said spatial light modulator produces an output image based upon said input color image data.
 33. The display system of claim 32 wherein said light emitter units comprise broad spectrum CCFL tubes.
 34. The display system of claim 32 wherein said light emitter units comprise broad spectrum LED emitters.
 35. The display system of claim 32 wherein said light emitter units comprise a set of individually addressable colored LED emitters, said set capable of emitting broad spectrum light.
 36. The display system of claim 32 wherein said spatial light modulator comprises a monochrome LCD display.
 37. The display system of claim 32 wherein said spatial light modulator comprises a multiprimary LCD display, said multiprimary LCD display further substantially comprises a plurality of a subpixel repeating group, said group further comprising a set of colored subpixels. 